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- note about mpi-local dmpi storage for get_image() git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@8021 b3059339-0415-0410-9bf9-f77b7e298cf2
351 lines
15 KiB
Plaintext
351 lines
15 KiB
Plaintext
The libMPcodecs API details, hints - by A'rpi
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==================================
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See also: colorspaces.txt, codec-devel.txt, dr-methods.txt, codecs.conf.txt
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The VIDEO path:
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===============
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[MPlayer core]
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| (1)
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_____V______ (2) /~~~~~~~~~~\ (3,4) |~~~~~~|
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| | -----> | vd_XXX.c | -------> | vd.c |
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| decvideo | \__________/ <-(3a)-- |______|
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| | -----, ,.............(3a,4a).....:
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~~~~~~~~~~~~ (6) V V
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/~~~~~~~~\ /~~~~~~~~\ (8)
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| vf_X.c | --> | vf_Y.c | ----> vf_vo.c / ve_XXX.c
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\________/ \________/
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| ^
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(7) | |~~~~~~| : (7a)
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`-> | vf.c |...:
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|______|
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Short description of video path:
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1. mplayer/mencoder core requests the decoding of a compressed video frame:
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calls decvideo.c::decode_video()
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2. decode_video() calls the previously ( init_video() ) selected video codec
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(vd_XXXX.c file, where XXXX == vfm name, see the 'driver' line of codecs.conf)
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3. the codec should initialize output device before decoding the first frame,
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it may happen in init() or at the middle of the first decode(). see 3.a.
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it means calling vd.c::mpcodecs_config_vo() with the image dimensions,
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and the _preferred_ (mean: internal, native, best) colorspace.
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NOTE: this colorspace may not be equal to the actually used colorspace, it's
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just a _hint_ for the csp matching algorithm, and mainly used _only_ when
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csp conversion is required, as input format of the converter.
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3.a. selecting the best output colorspace:
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the vd.c::mpcodecs_config_vo() function will go through the outfmt list
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defined by codecs.conf's 'out' lines, and query both vd (codec) and vo
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(output device/filter/encoder) if it's supported or not.
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For the vo, it calls the query_format() func of vf_XXX.c or ve_XXX.c.
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It should return a set of feature flags, the most important ons for this
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stage are: VFCAP_CSP_SUPPORTED (csp supported directly or by conversion)
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and VFCAP_CSP_SUPPORTED_BY_HW (csp supported WITHOUT any conversion).
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For the vd (codec), control() with VDCTRL_QUERY_FORMAT will be called.
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If it doesn't implement VDCTRL_QUERY_FORMAT, (ie answers CONTROL_UNKNOWN
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or CONTROL_NA) it will be assumed to be CONTROL_TRUE (csp supported)!
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So, by default, if the list of supported colorspaces is constant, doesn't
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depend on the actual file's/stream's header, it's enough to list them
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in codecs.conf ('out' field), and don't implement VDCTRL_QUERY_FORMAT.
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It's the case for the most codecs.
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If the supported csp list depends on the file being decoded, list the
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possible out formats (colorspaces) in codecs.conf, and implement the
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VDCTRL_QUERY_FORMAT to test the availability of the given csp for the
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given video file/stream.
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The vd.c core will find the best matching colorspace, depending on the
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VFCAP_CSP_SUPPORTED_BY_HW flag (see vfcap.h). If no match at all, it
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will try again with the 'scale' filter inserted between vd and vo.
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If still no match, it will fail :(
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4. requesting buffer for the decoded frame:
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The codec have to call mpcodecs_get_image() with proper imgtype & imgflag.
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It will find the optimal buffering setup (preferred stride, alignment etc)
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and return a pointer to the allocated and filled up mpi (mp_image_t*) struct.
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The 'imgtype' controls the buffering setup, ie STATIC (just one buffer,
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it 'remembers' its contents between frames), TEMP (write-only, full update),
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EXPORT (memory allocation is done by the codec, not recommended) and so on.
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The 'imgflags' set up the limits for the buffer, ie stride limitations,
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readability, remembering content etc. See mp_image.h for the short descr.
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See dr-methods.txt for the explanation of buffer importing and mpi imgtypes.
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Always try to implement stride support! (stride == bytes per line)
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If no stride support, then stride==bytes_per_pixel*image_width.
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If you have stride supoprt in your decoder, use the mpi->stride[] value
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for the byte_per_line for each plane.
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Also take care of other imgflags, like MP_IMGFLAG_PRESERVE and
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MP_IMGFLAG_READABLE, MP_IMGFLAG_COMMON_STRIDE and MP_IMGFLAG_COMMON_PLANE!
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The file mp_image.h contains description of flags in comments, read it!
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Ask for help on -dev-eng, describing the behaviour your codec, if unsure.
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4.a. buffer allocation, vd.c::mpcodecs_get_image():
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If the requested buffer imgtype!=EXPORT, then vd.c will try to do
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direct rendering, ie. asks the next filter/vo for the buffer allocation.
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It's done by calling get_image() of the vf_XXX.c file.
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If it was successful, the imgflag MP_IMGFLAG_DIRECT will be set, and one
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memcpy() will be saved when passing the data from vd to the next filter/vo.
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See dr-methods.txt for details and examples.
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5. decode the frame, to the mpi structure requested at 4, then return the mpi
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to decvideo.c. Return NULL if the decoding failed or skipped frame.
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6. decvideo.c::decode_video() will now pass the 'mpi' to the next filter (vf_X).
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7. the filter's (vf_X) put_image() then requests a new mpi buffer by calling
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vf.c::vf_get_image().
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7.a. vf.c::vf_get_image() will try to get direct rendering, by asking the
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next fliter to do the buffer allocation (calls vf_Y's get_image()).
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if it fails, it will fallback to normal system memory allocation.
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8. when we're over the whole filter chain (multiple filters can be connected,
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even the same filter multiple times) then the last, 'leaf' filter will be
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called. The only difference between leaf and non-leaf filter is that leaf
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filter have to implement the whole filter api.
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Leaf filters are now: vf_vo.c (wrapper over libvo) and ve_XXX.c (video
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encoders used by mencoder).
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The VIDEO FILTER API:
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=====================
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filename: vf_FILTERNAME.c
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vf_info_t* info;
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pointer to the filter description structure:
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const char *info; // description of the filter
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const char *name; // short name of the filter, must be FILTERNAME
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const char *author; // name and email/url of the author(s)
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const char *comment;// comment, url to papers describing algo etc.
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int (*open)(struct vf_instance_s* vf,char* args);
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// pointer to the open() function:
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Sample:
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vf_info_t vf_info_foobar = {
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"Universal Foo and Bar filter",
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"foobar",
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"Ms. Foo Bar",
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"based on algo described at http://www.foo-bar.org",
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open
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};
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The open() function:
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open() is called when the filter is appended/inserted to the filter chain.
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it'll receive the handler (vf) and the optional filter parameters as
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char* string. Note, that encoders (ve_*) and vo wrapper (vf_vo.c) have
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non-string arg, but it's specially handled by mplayer/mencoder.
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The open() function should fill the vf_instance_t structure, with the
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implemented functions' pointers (see bellow).
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It can optinally allocate memory for its internal data (vf_priv_t) and
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store the pointer in vf->priv.
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The open() func should parse (or at least check syntax) of parameters,
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and fail (return 0) if error.
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Sample:
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static int open(vf_instance_t *vf, char* args){
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vf->query_format=query_format;
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vf->config=config;
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vf->put_image=put_image;
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// allocate local storage:
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vf->priv=malloc(sizeof(struct vf_priv_s));
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vf->priv->w=
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vf->priv->h=-1;
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if(args) // parse args:
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if(sscanf(args, "%d:%d", &vf->priv->w, &vf->priv->h)!=2) return 0;
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return 1;
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}
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Functions in vf_instance_s:
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NOTE: All these are optional, their func pointer is either NULL or points to
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a default implementation. If you implement them, don't forget to set
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vf->FUNCNAME in your open() !
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int (*query_format)(struct vf_instance_s* vf,
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unsigned int fmt);
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The query_format() func. is called one or more times before the config(),
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to find out the capabilities and/or support status of a given colorspace (fmt).
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For the return values, see vfcap.h!
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Normally, a filter should return at least VFCAP_CSP_SUPPORTED for all supported
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colorspaces it accepts as input, and 0 for the unsupported ones.
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If your filter does linear conversion, it should query the next filter,
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and merge in its capability flags. Note: you should always ensure that the
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next filter will accept at least one of your possible output colorspaces!
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Sample:
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static int query_format(struct vf_instance_s* vf, unsigned int fmt){
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switch(fmt){
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case IMGFMT_YV12:
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case IMGFMT_I420:
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case IMGFMT_IYUV:
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case IMGFMT_422P:
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return vf_next_query_format(vf,IMGFMT_YUY2) & (~VFCAP_CSP_SUPPORTED_BY_HW);
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}
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return 0;
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}
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For the more complex case, when you have an N->M colorspace mapping matrix,
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see vf_scale or vf_rgb2bgr for examples.
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int (*config)(struct vf_instance_s* vf,
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int width, int height, int d_width, int d_height,
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unsigned int flags, unsigned int outfmt);
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The config() is called to initialize/confugre the filter before using it.
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Its parameters are already well-known from libvo:
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width, height: size of the coded image
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d_width, d_height: wanted display size (usually aspect corrected w/h)
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Filters should use width,height as input image dimension, but the
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resizing filters (crop, expand, scale, rotate, etc) should update
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d_width/d_height (display size) to preserve the correct aspect ratio!
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Filters should not rely on d_width, d_height as input parameters,
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the only exception is when a filter replaces some libvo functionality
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(like -vop scale with -zoom, or OSD rendering wiht -vop expand).
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flags: the "good" old flags set of libvo:
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0x01 - force fullscreen (-fs)
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0x02 - allow mode switching (-vm)
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0x04 - allow software scaling (-zoom)
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0x08 - flipping (-flip)
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(Usually you don't have to worry about flags, just pass it to next config.)
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outfmt: the selected colorspace/pixelformat. You'll receive images in this
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format.
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Sample:
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static int config(struct vf_instance_s* vf,
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int width, int height, int d_width, int d_height,
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unsigned int flags, unsigned int outfmt){
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// use d_width/d_height if not set by user:
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if(vf->priv->w==-1) vf->priv->w=d_width;
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if(vf->priv->h==-1) vf->priv->h=d_width;
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// initialize your filter code
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...
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// ok now config the rest of the filter chain, with our output parameters:
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return vf_next_config(vf,vf->priv->w,vf->priv->h,d_width,d_height,flags,outfmt);
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}
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void (*uninit)(struct vf_instance_s* vf);
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Okey, uninit() is the simplest, it's called at the end. You can free your
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private buffers etc here.
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int (*put_image)(struct vf_instance_s* vf,
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mp_image_t *mpi);
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Ah, put_image(). This is the main filter function it should convert/filter/
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transform the image data from one format/size/color/whatever to another.
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Its input parameter is an mpi (mplayer image) structure, see mp_image.h.
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Your filter has to request a new image buffer for the output, using the
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vf_get_image() function. NOTE: even if you don't want to modify the image,
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just pass it to the next filter, you have to either
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- do not implement put_image() at all - then it will be skipped
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- request a new image with type==EXPORT and copy the pointers
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NEVER pass the mpi as-is, it's local to filters and may cause trouble.
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If you completely copy/transform the image, then you probably want this:
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dmpi=vf_get_image(vf->next,mpi->imgfmt,
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MP_IMGTYPE_TEMP, MP_IMGFLAG_ACCEPT_STRIDE,
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vf->priv->w, vf->priv->h);
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It will allocate a new image, and return an mp_image structure filled by
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buffer pointers and stride (bytes per line) values, in size of vf->priv->w
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times vf->priv->h. If your filter cannot handle stride, then left out
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MP_IMGFLAG_ACCEPT_STRIDE. Note, that you can do this, but it isn't recommended,
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the whole video path is designed to use strides to get optimal throughput.
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If your filter allocates output image buffers, then use MP_IMGTYPE_EXPORT,
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and fill the returned dmpi's planes[], stride[] with your buffer parameters.
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Note, it is not recommended (no direct rendering), so if you can, use
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vf_get_image() for buffer allocation!
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For other image types and flags see mp_image.h, it has comments.
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If you are unsure, feel free to ask on the -dev-eng maillist. Please
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describe the behaviour of your filter, an dits limitations, so we can
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suggest the optimal buffer type + flags for your code.
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Now, that you have the input (mpi) and output (dmpi) buffers, you can do
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the conversion. If you didn't notice yet, mp_image has some useful info
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fields, may help you a lot creating if() or for() structures:
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flags: MP_IMGFLAG_PLANAR, MP_IMGFLAG_YUV, MP_IMGFLAG_SWAPPED
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helps you to handle various pixel formats in single code.
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bpp: bits per pixel
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WARNING! It's number of bits _allocated_ to store a pixel,
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it is not the number of bits actually used to keep colors!
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So, it's 16 for both 15 and 16bit color depth, and is 32 for
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32bpp (actually 24bit color depth) mode!
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It's 1 for 1bpp, 9 for YVU9, and is 12 for YV12 mode. Get it?
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For planar formats, you also have chroma_width, chroma_height and
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chroma_x_shift, chroma_y_shift too, they specify the chroma subsampling
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for yuv formats:
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chroma_width = luma_width >>chroma_x_shift;
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chroma_height= luma_height>>chroma_y_shift;
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If you're done, call the rest of the filter chain to process your output
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image:
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return vf_next_put_image(vf,dmpi);
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Ok, the rest is for advanced functionality only:
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int (*control)(struct vf_instance_s* vf,
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int request, void* data);
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You can control the filter in runtime from mplayer/mencoder/dec_video:
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#define VFCTRL_QUERY_MAX_PP_LEVEL 4 /* test for postprocessing support (max level) */
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#define VFCTRL_SET_PP_LEVEL 5 /* set postprocessing level */
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#define VFCTRL_SET_EQUALIZER 6 /* set color options (brightness,contrast etc) */
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#define VFCTRL_GET_EQUALIZER 8 /* gset color options (brightness,contrast etc) */
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#define VFCTRL_DRAW_OSD 7
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#define VFCTRL_CHANGE_RECTANGLE 9 /* Change the rectangle boundaries */
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void (*get_image)(struct vf_instance_s* vf,
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mp_image_t *mpi);
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This is for direct rendering support, works the same way as in libvo drivers.
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It makes in-place pixel modifications possible.
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If you implement it (vf->get_image!=NULL) then it will be called to do the
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buffer allocation. You SHOULD check the buffer restrictions (stride, type,
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readability etc) and if all OK, then allocate the requested buffer using
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the vf_get_image() func and copying the buffer pointers.
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NOTE: You HAVE TO save dmpi pointer, as you'll need it in put_image() later.
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It is not guaranteed that you'll get the same mpi for put_image() as in
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get_image() (think of out-of-order decoding, get_image is called in decoding
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order, while put_image is called for display) so the only safe place to save
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it is in the mpi struct itself: mpi->priv=(void*)dmpi;
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void (*draw_slice)(struct vf_instance_s* vf,
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unsigned char** src, int* stride, int w,int h, int x, int y);
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It's the good old draw_slice callback, already known from libvo.
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If your filter can operate on partial images, you can implement this one
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to improve performance (cache utilization).
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Ah, and there is two set of capability/requirement flags (vfcap.h type)
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in vf_instance_t, used by default query_format() implementation, and by
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the automatic colorspace/stride matching code (vf_next_config()).
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// caps:
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unsigned int default_caps; // used by default query_format()
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unsigned int default_reqs; // used by default config()
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The AUDIO path:
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===============
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TODO!!!
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