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added reference to codecs related .txt files git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@6849 b3059339-0415-0410-9bf9-f77b7e298cf2
98 lines
4.2 KiB
Plaintext
98 lines
4.2 KiB
Plaintext
6. libao2: this control audio playing
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As in libvo (see 5.) also here are some drivers, based on the same API:
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static int control(int cmd, int arg);
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This is for reading/setting driver-specific and other special parameters.
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Not really used for now.
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static int init(int rate,int channels,int format,int flags);
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The init of driver, opens device, sets sample rate, channels, sample format
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parameters.
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Sample format: usually AFMT_S16_LE or AFMT_U8, for more definitions see
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dec_audio.c and linux/soundcards.h files!
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static void uninit();
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Guess what.
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Ok I help: closes the device, not (yet) called when exit.
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static void reset();
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Resets device. To be exact, it's for deleting buffers' contents,
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so after reset() the previously received stuff won't be output.
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(called if pause or seek)
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static int get_space();
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Returns how many bytes can be written into the audio buffer without
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blocking (making caller process wait). If the buffer is (nearly) full,
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has to return 0!
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If it never gives 0, MPlayer won't work!
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static int play(void* data,int len,int flags);
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Plays a bit of audio, which is received throught the "data" memory area, with
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a size of "len". The "flags" isn't used yet. It has to copy the data, because
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they can be overwritten after the call is made. Doesn't really have to use
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all the bytes, it has to give back how many have been used (copied to
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buffer).
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static float get_delay();
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Returns how long time it will take to play the data currently in the
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output buffer. Be exact, if possible, since the whole timing depends
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on this! In the worst case, return the maximum delay.
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!!! Because the video is synchronized to the audio (card), it's very important
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!!! that the get_space and get_delay functions are correctly implemented!
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6.a audio plugins
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Audio plugins are used for processing the audio data before it
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reaches the soundcard driver. A plugin can change the following
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aspects of the audio data stream:
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1. Sample format
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2. Sample rate
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3. Number of channels
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4. The data itself (i.e. filtering and other sound effects)
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5. The delay (almost all plugins does this)
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The plugin interface is implemented as a pseudo device driver with
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the catchy name "plugin". The plugins are executed sequentially
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ordered by the "-aop list=plugin1,plugin2,..." command line switch.
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To add plugins add an entry in audio_plugin.h the makefile and
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create a source file named "pl_whatever.c". Input parameters are
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added to audio_plugin.h and to cfg-mplayer.h. A good starting point
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for writing plugins is pl_delay.c. Below is a description of what
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the functions does:
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static int control(int cmd, int arg);
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This is for reading/setting plugin-specific and other special
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parameters and can be used for keyboard input for example. All
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plugins bust respond to cmd=AOCONTROL_PLUGIN_SET_LEN which is part
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of the initialization of the plugin. When this command is received
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the parameter pl_delay.len will contain the maximum size of data the
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plugin can produce. This can be used for calculating and allocating
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buffer space for the plugin. Before the function exits the parameter
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pl_delay.len must be set to the maximum data size the plugin can
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receive. Return CONTROL_OK for success and CONTROL_ERROR for fail,
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other control codes are found in audio_out.h.
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static int init();
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This function is for initializing the plugin, it is called once
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before the playing is started. In this function the plugin can read
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AND write to the ao_plugin_data struct to determine and set input
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and output parameters. It is important to write to the
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ao_plugin_data.sz_mult and ao_plugin_data.delay_fix parameters if
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the plugin changes the data size or adds delay. Return 0 for fail
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and 1 for success.
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static void uninit()
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Called before mplayer exits. Used for deallocating dynamic buffers.
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static void reset()
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Called during reset can be used to empty buffers. Mplayer calls this
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function when pause is pressed.
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static int play()
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Called for every block of audio data sent through the plugin. This
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function should be optimized for speed. The incoming data is found
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in ao_plugin_data.data having length ao_plugin_data.len. These two
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parameters should be changed by the plugin. Return 1 for success and
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0 for fail.
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