mpv/libmpv/client.h

/* Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
 * Note: the client API is licensed under ISC (see above) to ease
 * interoperability with other licenses. But keep in mind that the
 * mpv core is still mostly GPLv2+. It's up to lawyers to decide
 * whether applications using this API are affected by the GPL.
 * One argument against this is that proprietary applications
 * using mplayer in slave mode is apparently tolerated, and this
 * API is basically equivalent to slave mode.
 */

#ifndef MPV_CLIENT_API_H_
#define MPV_CLIENT_API_H_

#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif

/**
 * Mechanisms provided by this API
 * -------------------------------
 *
 * This API provides general control over mpv playback. It does not give you
 * direct access to individual components of the player, only the whole thing.
 * It's somewhat equivalent to MPlayer's slave mode. You can send commands,
 * retrieve or set playback status or settings with properties, and receive
 * events.
 *
 * The API can be used in two ways:
 * 1) Internally in mpv, to provide additional features to the command line
 *    player. Lua scripting uses this. (Currently there is no plugin API to
 *    get a client API handle in external user code. It has to be a fixed
 *    part of the player at compilation time.)
 * 2) Using mpv as a library with mpv_create(). This basically allows embedding
 *    mpv in other applications.
 *
 * Event loop
 * ----------
 *
 * In general, the API user should run an event loop in order to receive events.
 * This even loop should call mpv_wait_event(), which will return once a new
 * mpv client API is available. It should also be possible to integrate client
 * API usage in other event loops (e.g. GUI toolkits) with the
 * mpv_set_wakeup_callback() function, and then polling for events by calling
 * mpv_wait_event() with a 0 timeout.
 *
 * Note that the event loop is detached from the actual player. Not calling
 * mpv_wait_event() will not stop playback. It will eventually congest the
 * event queue of your API handle, though.
 *
 * Synchronous vs. asynchronous calls
 * ----------------------------------
 *
 * The API allows both synchronous and asynchronous calls. Synchronous calls
 * have to wait until the playback core is ready, which currently can take
 * an unbounded time (e.g. if network is slow or unresponsive). Asynchronous
 * calls just queue operations as requests, and return the result of the
 * operation as events.
 *
 * Asynchronous calls
 * ------------------
 *
 * The client API includes asynchronous functions. These allow you to send
 * requests instantly, and get replies as events at a later point. The
 * requests are made with functions carrying the _async suffix, and replies
 * are returned by mpv_wait_event() (interleaved with the normal event stream).
 *
 * A 64 bit userdata value is used to allow the user to associate requests
 * with replies. The value is passed as reply_userdata parameter to the request
 * function. The reply to the request will have the reply
 * mpv_event->reply_userdata field set to the same value as the
 * reply_userdata parameter of the corresponding request.
 *
 * This userdata value is arbitrary and is never interpreted by the API. Note
 * that the userdata value 0 is also allowed, but then the client must be
 * careful not accidentally interpret the mpv_event->reply_userdata if an
 * event is not a reply. (For non-replies, this field is set to 0.)
 *
 * Currently, asynchronous calls are always strictly ordered (even with
 * synchronous calls) for each client, although that may change in the future.
 *
 * Multithreading
 * --------------
 *
 * The client API is generally fully thread-safe, unless otherwise noted.
 * Currently, there is no real advantage in using more than 1 thread to access
 * the client API, since everything is serialized through a single lock in the
 * playback core.
 *
 * Basic environment requirements
 * ------------------------------
 *
 * This documents basic requirements on the C environment. This is especially
 * important if mpv is used as library with mpv_create().
 *
 * - The LC_NUMERIC locale category must be set to "C". If your program calls
 *   setlocale(), be sure not to use LC_ALL, or if you do, reset LC_NUMERIC
 *   to its sane default: setlocale(LC_NUMERIC, "C").
 * - If a X11 based VO is used, mpv will set the xlib error handler. This error
 *   handler is process-wide, and there's no proper way to share it with other
 *   xlib users within the same process. This might confuse GUI toolkits.
 * - mpv uses some other libraries that are not library-safe, such as Fribidi
 *   (used through libass), ALSA, FFmpeg, and possibly more.
 * - The FPU precision must be set at least to double precision.
 * - On Windows, mpv will call timeBeginPeriod(1).
 * - On memory exhaustion, mpv will kill the process.
 *
 * Embedding the video window
 * --------------------------
 *
 * Currently you have to get the raw window handle, and set it as "wid" option.
 * This works on X11 and win32 only. In addition, it works with a few VOs only,
 * and VOs which do not support this will just create a freestanding window.
 *
 * Both on X11 and win32, the player will fill the window referenced by the
 * "wid" option fully and letterbox the video (i.e. add black bars if the
 * aspect ratio of the window and the video mismatch).
 *
 * On OSX, embedding is not yet possible, because Cocoa makes this non-trivial.
 *
 * Compatibility
 * -------------
 *
 * mpv development doesn't stand still, and changes to mpv internals as well as
 * to its interface can cause compatibility issues to client API users.
 *
 * The API is versioned (see MPV_CLIENT_API_VERSION), and changes to it are
 * documented in DOCS/client-api-changes.rst. The C API itself will probably
 * remain compatible for a long time, but the functionality exposed by it
 * could change more rapidly. For example, it's possible that options are
 * renamed, or change the set of allowed values.
 *
 * Defensive programming should be used to potentially deal with the fact that
 * options, commands, and properties could disappear, change their value range,
 * or change the underlying datatypes. It might be a good idea to prefer
 * MPV_FORMAT_STRING over other types to decouple your code from potential
 * mpv changes.
 */

/**
 * The version is incremented on each API change. The 16 lower bits form the
 * minor version number, and the 16 higher bits the major version number. If
 * the API becomes incompatible to previous versions, the major version
 * number is incremented. This affects only C part, and not properties and
 * options.
 *
 * You can use MPV_MAKE_VERSION() and compare the result with integer
 * relational operators (<, >, <=, >=).
 */
#define MPV_MAKE_VERSION(major, minor) (((major) << 16) | (minor) | 0UL)
#define MPV_CLIENT_API_VERSION MPV_MAKE_VERSION(1, 8)

/**
 * Return the MPV_CLIENT_API_VERSION the mpv source has been compiled with.
 */
unsigned long mpv_client_api_version(void);

/**
 * Client context used by the client API. Every client has its own private
 * handle.
 */
typedef struct mpv_handle mpv_handle;

/**
 * List of error codes than can be returned by API functions. 0 and positive
 * return values always mean success, negative values are always errors.
 */
typedef enum mpv_error {
    /**
     * No error happened (used to signal successful operation).
     * Keep in mind that many API functions returning error codes can also
     * return positive values, which also indicate success. API users can
     * hardcode the fact that ">= 0" means success.
     */
    MPV_ERROR_SUCCESS           = 0,
    /**
     * The event ringbuffer is full. This means the client is choked, and can't
     * receive any events. This can happen when too many asynchronous requests
     * have been made, but not answered. Probably never happens in practice,
     * unless the mpv core is frozen for some reason, and the client keeps
     * making asynchronous requests. (Bugs in the client API implementation
     * could also trigger this, e.g. if events become "lost".)
     */
    MPV_ERROR_EVENT_QUEUE_FULL = -1,
    /**
     * Memory allocation failed.
     */
    MPV_ERROR_NOMEM             = -2,
    /**
     * The mpv core wasn't configured and initialized yet. See the notes in
     * mpv_create().
     */
    MPV_ERROR_UNINITIALIZED     = -3,
    /**
     * Generic catch-all error if a parameter is set to an invalid or
     * unsupported value. This is used if there is no better error code.
     */
    MPV_ERROR_INVALID_PARAMETER = -4,
    /**
     * Trying to set an option that doesn't exist.
     */
    MPV_ERROR_OPTION_NOT_FOUND  = -5,
    /**
     * Trying to set an option using an unsupported MPV_FORMAT.
     */
    MPV_ERROR_OPTION_FORMAT     = -6,
    /**
     * Setting the option failed. Typically this happens if the provided option
     * value could not be parsed.
     */
    MPV_ERROR_OPTION_ERROR      = -7,
    /**
     * The accessed property doesn't exist.
     */
    MPV_ERROR_PROPERTY_NOT_FOUND = -8,
    /**
     * Trying to set or get a property using an unsupported MPV_FORMAT.
     */
    MPV_ERROR_PROPERTY_FORMAT   = -9,
    /**
     * The property exists, but is not available. This usually happens when the
     * associated subsystem is not active, e.g. querying audio parameters while
     * audio is disabled.
     */
    MPV_ERROR_PROPERTY_UNAVAILABLE = -10,
    /**
     * Error setting or getting a property.
     */
    MPV_ERROR_PROPERTY_ERROR    = -11,
    /**
     * General error when running a command with mpv_command and similar.
     */
    MPV_ERROR_COMMAND           = -12
} mpv_error;

/**
 * Return a string describing the error. For unknown errors, the string
 * "unknown error" is returned.
 *
 * @param error error number, see enum mpv_error
 * @return A static string describing the error. The string is completely
 *         static, i.e. doesn't need to be deallocated, and is valid forever.
 */
const char *mpv_error_string(int error);

/**
 * General function to deallocate memory returned by some of the API functions.
 * Call this only if it's explicitly documented as allowed. Calling this on
 * mpv memory not owned by the caller will lead to undefined behavior.
 *
 * @param data A valid pointer returned by the API, or NULL.
 */
void mpv_free(void *data);

/**
 * Return the name of this client handle. Every client has its own unique
 * name, which is mostly used for user interface purposes.
 *
 * @return The client name. The string is read-only and is valid until the
 *         mpv_handle is destroyed.
 */
const char *mpv_client_name(mpv_handle *ctx);

/**
 * Create a new mpv instance and an associated client API handle to control
 * the mpv instance. This instance is in a pre-initialized state,
 * and needs to be initialized to be actually used with most other API
 * functions.
 *
 * Most API functions will return MPV_ERROR_UNINITIALIZED in the uninitialized
 * state. You can call mpv_set_option() (or mpv_set_option_string() and other
 * variants) to set initial options. After this, call mpv_initialize() to start
 * the player, and then use e.g. mpv_command() to start playback of a file.
 *
 * The point of separating handle creation and actual initialization is that
 * you can configure things which can't be changed during runtime.
 *
 * Unlike the command line player, this will have initial settings suitable
 * for embedding in applications. The following settings are different:
 * - stdin/stdout/stderr and the terminal will never be accessed. This is
 *   equivalent to setting the --no-terminal option.
 *   (Technically, this also suppresses C signal handling.)
 * - No config files will be loaded. This is roughly equivalent to using
 *   --no-config (but actually the code path for loading config files is
 *   disabled).
 * - Idle mode is enabled, which means the playback core will enter idle mode
 *   if there are no more files to play on the internal playlist, instead of
 *   exiting. This is equivalent to the --idle option.
 * - Disable parts of input handling.
 *
 * All this assumes that API users want a mpv instance that is strictly
 * isolated from the command line player's configuration, user settings, and
 * so on. You can re-enable disabled features by setting the appropriate
 * options.
 *
 * The mpv command line parser is not available through this API, but you can
 * set individual options with mpv_set_option(). Files for playback must be
 * loaded with mpv_command() or others.
 *
 * Note that you should avoid doing concurrent accesses on the uninitialized
 * client handle. (Whether concurrent access is definitely allowed or not has
 * yet to be decided.)
 *
 * @return a new mpv client API handle
 */
mpv_handle *mpv_create(void);

/**
 * Initialize an uninitialized mpv instance. If the mpv instance is already
 * running, an error is retuned.
 *
 * This function needs to be called to make full use of the client API if the
 * client API handle was created with mpv_create().
 *
 * @return error code
 */
int mpv_initialize(mpv_handle *ctx);

/**
 * Disconnect and destroy the mpv_handle. ctx will be deallocated with this
 * API call. This leaves the player running. If you want to be sure that the
 * player is terminated, send a "quit" command, and wait until the
 * MPV_EVENT_SHUTDOWN event is received, or use mpv_terminate_destroy().
 */
void mpv_detach_destroy(mpv_handle *ctx);

/**
 * Similar to mpv_detach_destroy(), but brings the player and all clients down
 * as well, and waits until all of them are destroyed. This function blocks. The
 * advantage over mpv_detach_destroy() is that while mpv_detach_destroy() merely
 * detaches the client handle from the player, this function quits the player,
 * waits until all other clients are destroyed (i.e. all mpv_handles are
 * detached), and also waits for the final termination of the player.
 *
 * Since mpv_detach_destroy() is called somewhere on the way, it's not safe to
 * call other functions concurrently on the same context.
 *
 * If this is called on a mpv_handle that was not created with mpv_create(),
 * this function will merely send a quit command and then call
 * mpv_detach_destroy(), without waiting for the actual shutdown.
 */
void mpv_terminate_destroy(mpv_handle *ctx);

/**
 * Load a config file. This loads and parses the file, and sets every entry in
 * the config file's default section as if mpv_set_option_string() is called.
 *
 * The filename should be an absolute path. If it isn't, the actual path used
 * is unspecified. (Note: an absolute path starts with '/' on UNIX.) If the
 * file wasn't found, MPV_ERROR_INVALID_PARAMETER is returned.
 *
 * If a fatal error happens when parsing a config file, MPV_ERROR_OPTION_ERROR
 * is returned. Errors when setting options as well as other types or errors
 * are ignored (even if options do not exist). You can still try to capture
 * the resulting error messages with mpv_request_log_messages(). Note that it's
 * possible that some options were successfully set even if any of these errors
 * happen.
 *
 * The same restrictions as with mpv_set_option() apply: some options can't
 * be set outside of idle or uninitialized state, and many options don't
 * take effect immediately.
 *
 * @param filename absolute path to the config file on the local filesystem
 * @return error code
 */
int mpv_load_config_file(mpv_handle *ctx, const char *filename);

/**
 * Stop the playback thread. This means the core will stop doing anything, and
 * only run and answer to client API requests. This is sometimes useful; for
 * example, no new frame will be queued to the video output, so doing requests
 * which have to wait on the video output can run instantly.
 *
 * Suspension is reentrant and recursive for convenience. Any thread can call
 * the suspend function multiple times, and the playback thread will remain
 * suspended until the last thread resumes it. Note that during suspension, all
 * clients still have concurrent access to the core, which is serialized through
 * a single mutex.
 *
 * Call mpv_resume() to resume the playback thread. You must call mpv_resume()
 * for each mpv_suspend() call. Calling mpv_resume() more often than
 * mpv_suspend() is not allowed.
 *
 * Calling this on an uninitialized player (see mpv_create()) will deadlock.
 */
void mpv_suspend(mpv_handle *ctx);

/**
 * See mpv_suspend().
 */
void mpv_resume(mpv_handle *ctx);

/**
 * Return the internal time in microseconds. This has an arbitrary start offset,
 * but will never wrap or go backwards.
 *
 * Note that this is always the real time, and doesn't necessarily have to do
 * with playback time. For example, playback could go faster or slower due to
 * playback speed, or due to playback being paused. Use the "time-pos" property
 * instead to get the playback status.
 */
int64_t mpv_get_time_us(mpv_handle *ctx);

/**
 * Data format for options and properties. The API functions to get/set
 * properties and options support multiple formats, and this enum describes
 * them.
 */
typedef enum mpv_format {
    /**
     * Invalid. Sometimes used for empty values.
     */
    MPV_FORMAT_NONE             = 0,
    /**
     * The basic type is char*. It returns the raw property string, like
     * using ${=property} in input.conf (see input.rst).
     *
     * NULL isn't an allowed value.
     *
     * Warning: although the encoding is usually UTF-8, this is not always the
     *          case. File tags often store strings in some legacy codepage,
     *          and even filenames don't necessarily have to be in UTF-8 (at
     *          least on Linux). If you pass the strings to code that requires
     *          valid UTF-8, you have to sanitize it in some way.
     *
     * Example for reading:
     *
     *     char *result = NULL;
     *     if (mpv_get_property(ctx, "property", MPV_FORMAT_STRING, &result) < 0)
     *         goto error;
     *     printf("%s\n", result);
     *     mpv_free(result);
     *
     * Or just use mpv_get_property_string().
     *
     * Example for writing:
     *
     *     char *value = "the new value";
     *     // yep, you pass the address to the variable
     *     // (needed for symmetry with other types and mpv_get_property)
     *     mpv_set_property(ctx, "property", MPV_FORMAT_STRING, &value);
     *
     * Or just use mpv_set_property_string().
     *
     */
    MPV_FORMAT_STRING           = 1,
    /**
     * The basic type is char*. It returns the OSD property string, like
     * using ${property} in input.conf (see input.rst). In many cases, this
     * is the same as the raw string, but in other cases it's formatted for
     * display on OSD. It's intended to be human readable. Do not attempt to
     * parse these strings.
     *
     * Only valid when doing read access. The rest works like MPV_FORMAT_STRING.
     */
    MPV_FORMAT_OSD_STRING       = 2,
    /**
     * The basic type is int. The only allowed values are 0 ("no")
     * and 1 ("yes").
     *
     * Example for reading:
     *
     *     int result;
     *     if (mpv_get_property(ctx, "property", MPV_FORMAT_FLAG, &result) < 0)
     *         goto error;
     *     printf("%s\n", result ? "true" : "false");
     *
     * Example for writing:
     *
     *     int flag = 1;
     *     mpv_set_property(ctx, "property", MPV_FORMAT_STRING, &flag);
     */
    MPV_FORMAT_FLAG             = 3,
    /**
     * The basic type is int64_t.
     */
    MPV_FORMAT_INT64            = 4,
    /**
     * The basic type is double.
     */
    MPV_FORMAT_DOUBLE           = 5,
    /**
     * The type is mpv_node.
     *
     * For reading, you usually would pass a pointer to a stack-allocated
     * mpv_node value to mpv, and when you're done you call
     * mpv_free_node_contents(&node).
     * You're expected not to write to the data - if you have to, copy it
     * first (which you have to do manually).
     *
     * For writing, you construct your own mpv_node, and pass a pointer to the
     * API. The API will never write to your data (and copy it if needed), so
     * you're free to use any form of allocation or memory management you like.
     *
     * Warning: when reading, always check the mpv_node.format member. For
     *          example, properties might change their type in future versions
     *          of mpv, or sometimes even during runtime.
     *
     * Example for reading:
     *
     *     mpv_node result;
     *     if (mpv_get_property(ctx, "property", MPV_FORMAT_NODE, &result) < 0)
     *         goto error;
     *     printf("format=%d\n", (int)result.format);
     *     mpv_free_node_contents(&result).
     *
     * Example for writing:
     *
     *     mpv_node value;
     *     value.format = MPV_FORMAT_STRING;
     *     value.u.string = "hello";
     *     mpv_set_property(ctx, "property", MPV_FORMAT_NODE, &value);
     */
    MPV_FORMAT_NODE             = 6,
    /**
     * Used with mpv_node only. Can usually not be used directly.
     */
    MPV_FORMAT_NODE_ARRAY       = 7,
    /**
     * See MPV_FORMAT_NODE_ARRAY.
     */
    MPV_FORMAT_NODE_MAP         = 8
} mpv_format;

/**
 * Generic data storage.
 *
 * If mpv writes this struct (e.g. via mpv_get_property()), you must not change
 * the data. In some cases (mpv_get_property()), you have to free it with
 * mpv_free_node_contents(). If you fill this struct yourself, you're also
 * responsible for freeing it, and you must not call mpv_free_node_contents().
 */
typedef struct mpv_node {
    union {
        char *string;   /** valid if format==MPV_FORMAT_STRING */
        int flag;       /** valid if format==MPV_FORMAT_FLAG   */
        int64_t int64;  /** valid if format==MPV_FORMAT_INT64  */
        double double_; /** valid if format==MPV_FORMAT_DOUBLE */
        /**
         * valid if format==MPV_FORMAT_NODE_ARRAY
         *    or if format==MPV_FORMAT_NODE_MAP
         */
        struct mpv_node_list *list;
    } u;
    /**
     * Type of the data stored in this struct. This value rules what members in
     * the given union can be accessed. The following formats are currently
     * defined to be allowed in mpv_node:
     *
     *  MPV_FORMAT_STRING       (u.string)
     *  MPV_FORMAT_FLAG         (u.flag)
     *  MPV_FORMAT_INT64        (u.int64)
     *  MPV_FORMAT_DOUBLE       (u.double_)
     *  MPV_FORMAT_NODE_ARRAY   (u.list)
     *  MPV_FORMAT_NODE_MAP     (u.list)
     *  MPV_FORMAT_NONE         (no member)
     *
     * If you encounter a value you don't know, you must not make any
     * assumptions about the contents of union u.
     */
    mpv_format format;
} mpv_node;

/**
 * (see mpv_node)
 */
typedef struct mpv_node_list {
    /**
     * Number of entries. Negative values are not allowed.
     */
    int num;
    /**
     * MPV_FORMAT_NODE_ARRAY:
     *  values[N] refers to value of the Nth item
     *
     * MPV_FORMAT_NODE_MAP:
     *  values[N] refers to value of the Nth key/value pair
     *
     * If num > 0, values[0] to values[num-1] (inclusive) are valid.
     * Otherwise, this can be NULL.
     */
    mpv_node *values;
    /**
     * MPV_FORMAT_NODE_ARRAY:
     *  unused (typically NULL), access is not allowed
     *
     * MPV_FORMAT_NODE_MAP:
     *  keys[N] refers to key of the Nth key/value pair. If num > 0, keys[0] to
     *  keys[num-1] (inclusive) are valid. Otherwise, this can be NULL.
     *  The keys are in random order. The only guarantee is that keys[N] belongs
     *  to the value values[N]. NULL keys are not allowed.
     */
    char **keys;
} mpv_node_list;

/**
 * Frees any data referenced by the node. It doesn't free the node itself.
 * Call this only if the mpv client API set the node. If you constructed the
 * node yourself (manually), you have to free it yourself.
 *
 * If node->format is MPV_FORMAT_NONE, this call does nothing. Likewise, if
 * the client API sets a node with this format, this function doesn't need to
 * be called. (This is just a clarification that there's no danger of anything
 * strange happening in these cases.)
 */
void mpv_free_node_contents(mpv_node *node);

/**
 * Set an option. Note that you can't normally set options during runtime. It
 * works in uninitialized state (see mpv_create()), and in some cases in at
 * runtime.
 *
 * Changing options at runtime does not always work. For some options, attempts
 * to change them simply fails. Many other options may require reloading the
 * file for changes to take effect. In general, you should prefer calling
 * mpv_set_property() to change settings during playback, because the property
 * mechanism guarantees that changes take effect immediately.
 *
 * @param name Option name. This is the same as on the mpv command line, but
 *             without the leading "--".
 * @param format see enum mpv_format.
 * @param[in] data Option value (according to the format).
 * @return error code
 */
int mpv_set_option(mpv_handle *ctx, const char *name, mpv_format format,
                   void *data);

/**
 * Convenience function to set an option to a string value. This is like
 * calling mpv_set_option() with MPV_FORMAT_STRING.
 *
 * @return error code
 */
int mpv_set_option_string(mpv_handle *ctx, const char *name, const char *data);

/**
 * Send a command to the player. Commands are the same as those used in
 * input.conf, except that this function takes parameters in a pre-split
 * form.
 *
 * The commands and their parameters are documented in input.rst.
 *
 * @param[in] args NULL-terminated list of strings. Usually, the first item
 *                 is the command, and the following items are arguments.
 * @return error code
 */
int mpv_command(mpv_handle *ctx, const char **args);

/**
 * Same as mpv_command(), but allows passing structured data in any format.
 * In particular, calling mpv_command() is exactly like calling
 * mpv_command_node() with the format set to MPV_FORMAT_NODE_ARRAY, and
 * every arg passed in order as MPV_FORMAT_STRING.
 *
 * @param[in] args mpv_node with format set to MPV_FORMAT_NODE_ARRAY; each entry
 *                 is an argument using an arbitrary format (the format must be
 *                 compatible to the used command). Usually, the first item is
 *                 the command name (as MPV_FORMAT_STRING).
 * @param[out] result Optional, pass NULL if unused. If not NULL, and if the
 *                    function succeeds, this is set to command-specific return
 *                    data. You must call mpv_free_node_contents() to free it
 *                    (again, only if the command actually succeeds).
 * @return error code (the result parameter is not set on error)
 */
int mpv_command_node(mpv_handle *ctx, mpv_node *args, mpv_node *result);

/**
 * Same as mpv_command, but use input.conf parsing for splitting arguments.
 * This is slightly simpler, but also more error prone, since arguments may
 * need quoting/escaping.
 */
int mpv_command_string(mpv_handle *ctx, const char *args);

/**
 * Same as mpv_command, but run the command asynchronously.
 *
 * Commands are executed asynchronously. You will receive a
 * MPV_EVENT_COMMAND_REPLY event. (This event will also have an
 * error code set if running the command failed.)
 *
 * @param reply_userdata the value mpv_event.reply_userdata of the reply will
 *                       be set to (see section about asynchronous calls)
 * @param args NULL-terminated list of strings (see mpv_command())
 * @return error code (if parsing or queuing the command fails)
 */
int mpv_command_async(mpv_handle *ctx, uint64_t reply_userdata,
                      const char **args);

/**
 * Same as mpv_command_node(), but run it asynchronously. Basically, this
 * function is to mpv_command_node() what mpv_command_async() is to
 * mpv_command().
 *
 * See mpv_command_async() for details. Retrieving the result is not
 * supported yet.
 *
 * @param reply_userdata the value mpv_event.reply_userdata of the reply will
 *                       be set to (see section about asynchronous calls)
 * @param args as in mpv_command_node()
 * @return error code (if parsing or queuing the command fails)
 */
int mpv_command_node_async(mpv_handle *ctx, uint64_t reply_userdata,
                           mpv_node *args);

/**
 * Set a property to a given value. Properties are essentially variables which
 * can be queried or set at runtime. For example, writing to the pause property
 * will actually pause or unpause playback.
 *
 * If the format doesn't match with the internal format of the property, access
 * usually will fail with MPV_ERROR_PROPERTY_FORMAT. In some cases, the data
 * is automatically converted and access succeeds. For example, MPV_FORMAT_INT64
 * is always converted to MPV_FORMAT_DOUBLE, and access using MPV_FORMAT_STRING
 * usually invokes a string parser.
 *
 * @param name The property name. See input.rst for a list of properties.
 * @param format see enum mpv_format.
 * @param[in] data Option value.
 * @return error code
 */
int mpv_set_property(mpv_handle *ctx, const char *name, mpv_format format,
                     void *data);

/**
 * Convenience function to set a property to a string value.
 *
 * This is like calling mpv_set_property() with MPV_FORMAT_STRING.
 */
int mpv_set_property_string(mpv_handle *ctx, const char *name, const char *data);

/**
 * Set a property asynchronously. You will receive the result of the operation
 * as MPV_EVENT_SET_PROPERTY_REPLY event. The mpv_event.error field will contain
 * the result status of the operation. Otherwise, this function is similar to
 * mpv_set_property().
 *
 * @param reply_userdata see section about asynchronous calls
 * @param name The property name.
 * @param format see enum mpv_format.
 * @param[in] data Option value. The value will be copied by the function. It
 *                 will never be modified by the client API.
 * @return error code if sending the request failed
 */
int mpv_set_property_async(mpv_handle *ctx, uint64_t reply_userdata,
                           const char *name, mpv_format format, void *data);

/**
 * Read the value of the given property.
 *
 * If the format doesn't match with the internal format of the property, access
 * usually will fail with MPV_ERROR_PROPERTY_FORMAT. In some cases, the data
 * is automatically converted and access succeeds. For example, MPV_FORMAT_INT64
 * is always converted to MPV_FORMAT_DOUBLE, and access using MPV_FORMAT_STRING
 * usually invokes a string formatter.
 *
 * @param name The property name.
 * @param format see enum mpv_format.
 * @param[out] data Pointer to the variable holding the option value. On
 *                  success, the variable will be set to a copy of the option
 *                  value. For formats that require dynamic memory allocation,
 *                  you can free the value with mpv_free() (strings) or
 *                  mpv_free_node_contents() (MPV_FORMAT_NODE).
 * @return error code
 */
int mpv_get_property(mpv_handle *ctx, const char *name, mpv_format format,
                     void *data);

/**
 * Return the value of the property with the given name as string. This is
 * equivalent to mpv_get_property() with MPV_FORMAT_STRING.
 *
 * See MPV_FORMAT_STRING for character encoding issues.
 *
 * On error, NULL is returned. Use mpv_get_property() if you want fine-grained
 * error reporting.
 *
 * @param name The property name.
 * @return Property value, or NULL if the property can't be retrieved. Free
 *         the string with mpv_free().
 */
char *mpv_get_property_string(mpv_handle *ctx, const char *name);

/**
 * Return the property as "OSD" formatted string. This is the same as
 * mpv_get_property_string, but using MPV_FORMAT_OSD_STRING.
 *
 * @return Property value, or NULL if the property can't be retrieved. Free
 *         the string with mpv_free().
 */
char *mpv_get_property_osd_string(mpv_handle *ctx, const char *name);

/**
 * Get a property asynchronously. You will receive the result of the operation
 * as well as the property data with the MPV_EVENT_GET_PROPERTY_REPLY event.
 * You should check the mpv_event.error field on the reply event.
 *
 * @param reply_userdata see section about asynchronous calls
 * @param name The property name.
 * @param format see enum mpv_format.
 * @return error code if sending the request failed
 */
int mpv_get_property_async(mpv_handle *ctx, uint64_t reply_userdata,
                           const char *name, mpv_format format);

/**
 * Get a notification whenever the given property changes. You will receive
 * updates as MPV_EVENT_PROPERTY_CHANGE. Note that this is not very precise:
 * for some properties, it may not send updates even if the property changed.
 * This depends on the property, and it's a valid feature request to ask for
 * better update handling of a specific property. (For some properties, like
 * ``clock``, which shows the wall clock, this mechanism doesn't make too
 * much sense anyway.)
 *
 * Property changes are coalesced: the change events are returned only once the
 * event queue becomes empty (e.g. mpv_wait_event() would block or return
 * MPV_EVENT_NONE), and then only one event per changed property is returned.
 *
 * Normally, change events are sent only if the property value changes according
 * to the requested format. mpv_event_property will contain the property value
 * as data member.
 *
 * Warning: if a property is unavailable or retrieving it caused an error,
 *          MPV_FORMAT_NONE will be set in mpv_event_property, even if the
 *          format parameter was set to a different value. In this case, the
 *          mpv_event_property.data field is invalid.
 *
 * If the property is observed with the format parameter set to MPV_FORMAT_NONE,
 * you get low-level notifications whether the property _may_ have changed, and
 * the data member in mpv_event_property will be unset. With this mode, you
 * will have to determine yourself whether the property really changd. On the
 * other hand, this mechanism can be faster and uses less resources.
 *
 * Observing a property that doesn't exist is allowed. (Although it may still
 * cause some sporadic change events.)
 *
 * Keep in mind that you will get change notifications even if you change a
 * property yourself. Try to avoid endless feedback loops, which could happen
 * if you react to the change notifications triggered by your own change.
 *
 * @param reply_userdata This will be used for the mpv_event.reply_userdata
 *                       field for the received MPV_EVENT_PROPERTY_CHANGE
 *                       events. (Also see section about asynchronous calls,
 *                       although this function is somewhat different from
 *                       actual asynchronous calls.)
 *                       If you have no use for this, pass 0.
 *                       Also see mpv_unobserve_property().
 * @param name The property name.
 * @param format see enum mpv_format. Can be MPV_FORMAT_NONE to omit values
 *               from the change events.
 * @return error code (usually fails only on OOM or unsupported format)
 */
int mpv_observe_property(mpv_handle *mpv, uint64_t reply_userdata,
                         const char *name, mpv_format format);

/**
 * Undo mpv_observe_property(). This will remove all observed properties for
 * which the given number was passed as reply_userdata to mpv_observe_property.
 *
 * @param registered_reply_userdata ID that was passed to mpv_observe_property
 * @return negative value is an error code, >=0 is number of removed properties
 *         on success (includes the case when 0 were removed)
 */
int mpv_unobserve_property(mpv_handle *mpv, uint64_t registered_reply_userdata);

typedef enum mpv_event_id {
    /**
     * Nothing happened. Happens on timeouts or sporadic wakeups.
     */
    MPV_EVENT_NONE              = 0,
    /**
     * Happens when the player quits. The player enters a state where it tries
     * to disconnect all clients. Most requests to the player will fail, and
     * mpv_wait_event() will always return instantly (returning new shutdown
     * events if no other events are queued). The client should react to this
     * and quit with mpv_detach_destroy() as soon as possible.
     */
    MPV_EVENT_SHUTDOWN          = 1,
    /**
     * See mpv_request_log_messages().
     */
    MPV_EVENT_LOG_MESSAGE       = 2,
    /**
     * Reply to a mpv_get_property_async() request.
     * See also mpv_event and mpv_event_property.
     */
    MPV_EVENT_GET_PROPERTY_REPLY = 3,
    /**
     * Reply to a mpv_set_property_async() request.
     * (Unlike MPV_EVENT_GET_PROPERTY, mpv_event_property is not used.)
     */
    MPV_EVENT_SET_PROPERTY_REPLY = 4,
    /**
     * Reply to a mpv_command_async() request.
     */
    MPV_EVENT_COMMAND_REPLY     = 5,
    /**
     * Notification before playback start of a file (before the file is loaded).
     */
    MPV_EVENT_START_FILE        = 6,
    /**
     * Notification after playback end (after the file was unloaded).
     * See also mpv_event and mpv_event_end_file.
     */
    MPV_EVENT_END_FILE          = 7,
    /**
     * Notification when the file has been loaded (headers were read etc.), and
     * decoding starts.
     */
    MPV_EVENT_FILE_LOADED       = 8,
    /**
     * The list of video/audio/subtitle tracks was changed. (E.g. a new track
     * was found. This doesn't necessarily indicate a track switch; for this,
     * MPV_EVENT_TRACK_SWITCHED is used.)
     */
    MPV_EVENT_TRACKS_CHANGED    = 9,
    /**
     * A video/audio/subtitle track was switched on or off.
     */
    MPV_EVENT_TRACK_SWITCHED    = 10,
    /**
     * Idle mode was entered. In this mode, no file is played, and the playback
     * core waits for new commands. (The command line player normally quits
     * instead of entering idle mode, unless --idle was specified. If mpv
     * was started with mpv_create(), idle mode is enabled by default.)
     */
    MPV_EVENT_IDLE              = 11,
    /**
     * Playback was paused. This indicates the user pause state.
     *
     * The user pause state is the state the user requested (changed with the
     * "pause" property). There is an internal pause state too, which is entered
     * if e.g. the network is too slow (the "core-idle" property generally
     * indicates whether the core is playing or waiting).
     *
     * This event is sent whenever any pause states change, not only the user
     * state. You might get multiple events in a row while these states change
     * independently. But the event ID sent always indicates the user pause
     * state.
     *
     * If you don't want to deal with this, use mpv_observe_property() on the
     * "pause" property and ignore MPV_EVENT_PAUSE/UNPAUSE. Likewise, the
     * "core-idle" property tells you whether video is actually playing or not.
     */
    MPV_EVENT_PAUSE             = 12,
    /**
     * Playback was unpaused. See MPV_EVENT_PAUSE for not so obvious details.
     */
    MPV_EVENT_UNPAUSE           = 13,
    /**
     * Sent every time after a video frame is displayed. Note that currently,
     * this will be sent in lower frequency if there is no video, or playback
     * is paused - but that will be removed in the future, and it will be
     * restricted to video frames only.
     */
    MPV_EVENT_TICK              = 14,
    /**
     * Triggered by the script_dispatch input command. The command uses the
     * client name (see mpv_client_name()) to dispatch keyboard or mouse input
     * to a client.
     * (This is pretty obscure and largely replaced by MPV_EVENT_CLIENT_MESSAGE,
     * but still the only way to distinguish key down/up events when binding
     * script_dispatch via input.conf.)
     */
    MPV_EVENT_SCRIPT_INPUT_DISPATCH = 15,
    /**
     * Triggered by the script_message input command. The command uses the
     * first argument of the command as client name (see mpv_client_name()) to
     * dispatch the message, and passes along all arguments starting from the
     * second argument as strings.
     * See also mpv_event and mpv_event_client_message.
     */
    MPV_EVENT_CLIENT_MESSAGE    = 16,
    /**
     * Happens after video changed in some way. This can happen on resolution
     * changes, pixel format changes, or video filter changes. The event is
     * sent after the video filters and the VO are reconfigured. Applications
     * embedding a mpv window should listen to this event in order to resize
     * the window if needed.
     * Note that this event can happen sporadically, and you should check
     * yourself whether the video parameters really changed before doing
     * something expensive.
     */
    MPV_EVENT_VIDEO_RECONFIG    = 17,
    /**
     * Similar to MPV_EVENT_VIDEO_RECONFIG. This is relatively uninteresting,
     * because there is no such thing as audio output embedding.
     */
    MPV_EVENT_AUDIO_RECONFIG    = 18,
    /**
     * Happens when metadata (like file tags) is possibly updated. (It's left
     * unspecified whether this happens on file start or only when it changes
     * within a file.)
     */
    MPV_EVENT_METADATA_UPDATE   = 19,
    /**
     * Happens when a seek was initiated. Playback stops. Usually it will
     * resume with MPV_EVENT_PLAYBACK_RESTART as soon as the seek is finished.
     */
    MPV_EVENT_SEEK              = 20,
    /**
     * There was a discontinuity of some sort (like a seek), and playback
     * was reinitialized. Usually happens after seeking, or ordered chapter
     * segment switches. The main purpose is allowing the client to detect
     * when a seek request is finished.
     */
    MPV_EVENT_PLAYBACK_RESTART  = 21,
    /**
     * Event sent due to mpv_observe_property().
     * See also mpv_event and mpv_event_property.
     */
    MPV_EVENT_PROPERTY_CHANGE   = 22,
    /**
     * Happens when the current chapter changes.
     */
    MPV_EVENT_CHAPTER_CHANGE = 23
    // Internal note: adjust INTERNAL_EVENT_BASE when adding new events.
} mpv_event_id;

/**
 * Return a string describing the event. For unknown events, NULL is returned.
 *
 * Note that all events actually returned by the API will also yield a non-NULL
 * string with this function.
 *
 * @param event event ID, see see enum mpv_event_id
 * @return A static string giving a short symbolic name of the event. It
 *         consists of lower-case alphanumeric characters and can include "-"
 *         characters. This string is suitable for use in e.g. scripting
 *         interfaces.
 *         The string is completely static, i.e. doesn't need to be deallocated,
 *         and is valid forever.
 */
const char *mpv_event_name(mpv_event_id event);

typedef struct mpv_event_property {
    /**
     * Name of the property.
     */
    const char *name;
    /**
     * Format of the given data. See enum mpv_format.
     * This is always the same format as the requested format.
     */
    mpv_format format;
    /**
     * Received property value. Depends on the format. This is like the
     * pointer argument passed to mpv_get_property().
     *
     * For example, for MPV_FORMAT_STRING you get the string with:
     *
     *    char *value = *(char **)(event_property->data);
     *
     * Note that this is set to NULL if retrieving the property failed.
     * See mpv_event.error for the status.
     */
    void *data;
} mpv_event_property;

/**
 * Numeric log levels. The lower the number, the more important the message is.
 * MPV_LOG_LEVEL_NONE is never used when receiving messages. The string in
 * the comment after the value is the name of the log level as used for the
 * mpv_request_log_messages() function.
 */
typedef enum mpv_log_level {
    MPV_LOG_LEVEL_NONE  = 0,    /// "no"    - disable absolutely all messages
    MPV_LOG_LEVEL_FATAL = 10,   /// "fatal" - critical/aborting errors
    MPV_LOG_LEVEL_ERROR = 20,   /// "error" - simple errors
    MPV_LOG_LEVEL_WARN  = 30,   /// "warn"  - possible problems
    MPV_LOG_LEVEL_INFO  = 40,   /// "info"  - informational message
    MPV_LOG_LEVEL_V     = 50,   /// "v"     - noisy informational message
    MPV_LOG_LEVEL_DEBUG = 60,   /// "debug" - very noisy technical information
    MPV_LOG_LEVEL_TRACE = 70,   /// "trace" - extremely noisy
} mpv_log_level;

typedef struct mpv_event_log_message {
    /**
     * The module prefix, identifies the sender of the message. As a special
     * case, if the message buffer overflows, this will be set to the string
     * "overflow" (which doesn't appear as prefix otherwise), and the text
     * field will contain an informative message.
     */
    const char *prefix;
    /**
     * The log level as string. See mpv_request_log_messages() for possible
     * values. The level "no" is never used here.
     */
    const char *level;
    /**
     * The log message. It consists of 1 line of text, and is terminated with
     * a newline character. (Before API version 1.6, it could contain multiple
     * or partial lines.)
     */
    const char *text;
    /**
     * The same contents as the level field, but as a numeric ID.
     * Since API version 1.6.
     */
    mpv_log_level log_level;
} mpv_event_log_message;

typedef struct mpv_event_end_file {
    /**
     * Identifies the reason why playback was stopped:
     *  0: the end of the file was reached or initialization failed
     *  1: the file is restarted (e.g. edition switching)
     *  2: playback was aborted by an external action (e.g. playlist controls)
     *  3: the player received the quit command
     * Other values should be treated as unknown.
     */
  int reason;
} mpv_event_end_file;

typedef struct mpv_event_script_input_dispatch {
    /**
     * Arbitrary integer value that was provided as argument to the
     * script_dispatch input command.
     */
    int arg0;
    /**
     * Type of the input. Currently either "keyup_follows" (basically a key
     * down event), or "press" (either a single key event, or a key up event
     * following a "keyup_follows" event).
     */
    const char *type;
} mpv_event_script_input_dispatch;

typedef struct mpv_event_client_message {
    /**
     * Arbitrary arguments chosen by the sender of the message. If num_args > 0,
     * you can access args[0] through args[num_args - 1] (inclusive). What
     * these arguments mean is up to the sender and receiver.
     * None of the valid items are NULL.
     */
    int num_args;
    const char **args;
} mpv_event_client_message;

typedef struct mpv_event {
    /**
     * One of mpv_event. Keep in mind that later ABI compatible releases might
     * add new event types. These should be ignored by the API user.
     */
    mpv_event_id event_id;
    /**
     * This is mainly used for events that are replies to (asynchronous)
     * requests. It contains a status code, which is >= 0 on success, or < 0
     * on error (a mpv_error value). Usually, this will be set if an
     * asynchronous request fails.
     */
    int error;
    /**
     * If the event is in reply to a request (made with this API and this
     * API handle), this is set to the reply_userdata parameter of the request
     * call.
     * Otherwise, this field is 0.
     */
    uint64_t reply_userdata;
    /**
     * The meaning and contents of the data member depend on the event_id:
     *  MPV_EVENT_GET_PROPERTY_REPLY:     mpv_event_property*
     *  MPV_EVENT_PROPERTY_CHANGE:        mpv_event_property*
     *  MPV_EVENT_LOG_MESSAGE:            mpv_event_log_message*
     *  MPV_EVENT_SCRIPT_INPUT_DISPATCH:  mpv_event_script_input_dispatch*
     *  MPV_EVENT_CLIENT_MESSAGE:         mpv_event_client_message*
     *  MPV_EVENT_END_FILE:               mpv_event_end_file*
     *  other: NULL
     *
     * Note: future enhancements might add new event structs for existing or new
     *       event types.
     */
    void *data;
} mpv_event;

/**
 * Enable or disable the given event.
 *
 * Some events are enabled by default. Some events can't be disabled.
 *
 * (Informational note: currently, all events are enabled by default, except
 *  MPV_EVENT_TICK.)
 *
 * @param event See enum mpv_event_id.
 * @param enable 1 to enable receiving this event, 0 to disable it.
 * @return error code
 */
int mpv_request_event(mpv_handle *ctx, mpv_event_id event, int enable);

/**
 * Enable or disable receiving of log messages. These are the messages the
 * command line player prints to the terminal. This call sets the minimum
 * required log level for a message to be received with MPV_EVENT_LOG_MESSAGE.
 *
 * @param min_level Minimal log level as string. Valid log levels:
 *                      no fatal error warn info status v debug trace
 *                  The value "no" disables all messages. This is the default.
 *                  Also see mpv_log_level.
 */
int mpv_request_log_messages(mpv_handle *ctx, const char *min_level);

/**
 * Wait for the next event, or until the timeout expires, or if another thread
 * makes a call to mpv_wakeup(). Passing 0 as timeout will never wait, and
 * is suitable for polling.
 *
 * The internal event queue has a limited size (per client handle). If you
 * don't empty the event queue quickly enough with mpv_wait_event(), it will
 * overflow and silently discard further events. If this happens, making
 * asynchronous requests will fail as well (with MPV_ERROR_EVENT_QUEUE_FULL).
 *
 * Only one thread is allowed to call this at a time. The API won't complain
 * if more than one thread calls this, but it will cause race conditions in
 * the client when accessing the shared mpv_event struct. Note that most other
 * API functions are not restricted by this, and no API function internally
 * calls mpv_wait_event().
 *
 * @param timeout Timeout in seconds, after which the function returns even if
 *                no event was received. A MPV_EVENT_NONE is returned on
 *                timeout. A value of 0 will disable waiting. Negative values
 *                will wait with an infinite timeout.
 * @return A struct containing the event ID and other data. The pointer (and
 *         fields in the struct) stay valid until the next mpv_wait_event()
 *         call, or until the mpv_handle is destroyed. You must not write to
 *         the struct, and all memory referenced by it will be automatically
 *         released by the API. The return value is never NULL.
 */
mpv_event *mpv_wait_event(mpv_handle *ctx, double timeout);

/**
 * Interrupt the current mpv_wait_event() call. This will wake up the thread
 * currently waiting in mpv_wait_event(). If no thread is waiting, the next
 * mpv_wait_event() call will return immediately (this is to avoid lost
 * wakeups).
 *
 * mpv_wait_event() will receive a MPV_EVENT_NONE if it's woken up due to
 * this call. But note that this dummy event might be skipped if there are
 * already other events queued. All what counts is that the waiting thread
 * is woken up at all.
 */
void mpv_wakeup(mpv_handle *ctx);

/**
 * Set a custom function that should be called when there are new events. Use
 * this if blocking in mpv_wait_event() to wait for new events is not feasible.
 *
 * Keep in mind that the callback will be called from foreign threads. You
 * must not make any assumptions of the environment, and you must return as
 * soon as possible. You are not allowed to call any client API functions
 * inside of the callback. In particular, you should not do any processing in
 * the callback, but wake up another thread that does all the work. It's also
 * possible that the callback is called from a thread while a mpv API function
 * is called (i.e. it can be reentrant).
 *
 * In general, the client API expects you to call mpv_wait_event() to receive
 * notifications, and the wakeup callback is merely a helper utility to make
 * this easier in certain situations. Note that it's possible that there's
 * only one wakeup callback invocation for multiple events. You should call
 * mpv_wait_event() with no timeout until MPV_EVENT_NONE is reached, at which
 * point the event queue is empty.
 *
 * If you actually want to do processing in a callback, spawn a thread that
 * does nothing but call mpv_wait_event() in a loop and dispatches the result
 * to a callback.
 *
 * Only one wakeup callback can be set.
 *
 * @param cb function that should be called if a wakeup is required
 * @param d arbitrary userdata passed to cb
 */
void mpv_set_wakeup_callback(mpv_handle *ctx, void (*cb)(void *d), void *d);

/**
 * Return a UNIX file descriptor referring to the read end of a pipe. This
 * pipe can be used to wake up a poll() based processing loop. The purpose of
 * this function is very similar to mpv_set_wakeup_callback(), and provides
 * a primitive mechanism to handle coordinating a foreign event loop and the
 * libmpv event loop. The pipe is non-blocking. It's closed when the mpv_handle
 * is destroyed. This function always returns the same value (on success).
 *
 * This is in fact implemented using the same underlying code as for
 * mpv_set_wakeup_callback() (though they don't conflict), and it is as if each
 * callback invocation writes a single 0 byte to the pipe. When the pipe
 * becomes readable, the code calling poll() (or select()) on the pipe should
 * read all contents of the pipe and then call mpv_wait_event(c, 0) until
 * no new events are returned. The pipe contents do not matter and can just
 * be discarded. There is not necessarily one byte per readable event in the
 * pipe. For example, the pipes are non-blocking, and mpv won't block if the
 * pipe is full. Pipes are normally limited to 4096 bytes, so if there are
 * more than 4096 events, the number of readable bytes can not equal the number
 * of events queued. Also, it's possible that mpv does not write to the pipe
 * once it's guaranteed that the client was already signaled. See the example
 * below how to do it correctly.
 *
 * Example:
 *
 *  int pipefd = mpv_get_wakeup_pipe(mpv);
 *  if (pipefd < 0)
 *      error();
 *  while (1) {
 *      struct pollfd pfds[1] = {
 *          { .fd = pipefd, .events = POLLIN },
 *      };
 *      // Wait until there are possibly new mpv events.
 *      poll(pfds, 1, -1);
 *      if (pfds[0].revents & POLLIN) {
 *          // Empty the pipe. Doing this before calling mpv_wait_event()
 *          // ensures that no wakeups are missed. It's not so important to
 *          // make sure the pipe is really empty (it will just cause some
 *          // additional wakeups in unlikely corner cases).
 *          char unused[256];
 *          read(pipefd, unused, sizeof(unused));
 *          while (1) {
 *              mpv_event *ev = mpv_wait_event(mpv, 0);
 *              // If MPV_EVENT_NONE is received, the event queue is empty.
 *              if (ev->event_id == MPV_EVENT_NONE)
 *                  break;
 *              // Process the event.
 *              ...
 *          }
 *      }
 *  }
 *
 * @return A UNIX FD of the read end of the wakeup pipe, or -1 on error.
 *         On MS Windows/MinGW, this will always return -1.
 */
int mpv_get_wakeup_pipe(mpv_handle *ctx);

#ifdef __cplusplus
}
#endif

#endif