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444e9874a7
* commit 'def97856de':
lavc: AV-prefix all codec capabilities
Conflicts:
cmdutils.c
ffmpeg.c
ffplay.c
libavcodec/8svx.c
libavcodec/aacenc.c
libavcodec/ac3dec.c
libavcodec/adpcm.c
libavcodec/alac.c
libavcodec/atrac3plusdec.c
libavcodec/bink.c
libavcodec/dnxhddec.c
libavcodec/dvdec.c
libavcodec/dvenc.c
libavcodec/ffv1dec.c
libavcodec/ffv1enc.c
libavcodec/fic.c
libavcodec/flacdec.c
libavcodec/flacenc.c
libavcodec/flvdec.c
libavcodec/fraps.c
libavcodec/frwu.c
libavcodec/gifdec.c
libavcodec/h261dec.c
libavcodec/hevc.c
libavcodec/iff.c
libavcodec/imc.c
libavcodec/libopenjpegdec.c
libavcodec/libvo-aacenc.c
libavcodec/libvorbisenc.c
libavcodec/libvpxdec.c
libavcodec/libvpxenc.c
libavcodec/libx264.c
libavcodec/mjpegbdec.c
libavcodec/mjpegdec.c
libavcodec/mpegaudiodec_float.c
libavcodec/msmpeg4dec.c
libavcodec/mxpegdec.c
libavcodec/nvenc_h264.c
libavcodec/nvenc_hevc.c
libavcodec/pngdec.c
libavcodec/qpeg.c
libavcodec/ra288.c
libavcodec/rv10.c
libavcodec/s302m.c
libavcodec/sp5xdec.c
libavcodec/takdec.c
libavcodec/tiff.c
libavcodec/tta.c
libavcodec/utils.c
libavcodec/v210dec.c
libavcodec/vp6.c
libavcodec/vp9.c
libavcodec/wavpack.c
libavcodec/yop.c
Merged-by: Michael Niedermayer <michael@niedermayer.cc>
70 lines
3 KiB
Text
70 lines
3 KiB
Text
FFmpeg multithreading methods
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==============================================
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FFmpeg provides two methods for multithreading codecs.
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Slice threading decodes multiple parts of a frame at the same time, using
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AVCodecContext execute() and execute2().
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Frame threading decodes multiple frames at the same time.
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It accepts N future frames and delays decoded pictures by N-1 frames.
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The later frames are decoded in separate threads while the user is
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displaying the current one.
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Restrictions on clients
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==============================================
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Slice threading -
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* The client's draw_horiz_band() must be thread-safe according to the comment
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in avcodec.h.
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Frame threading -
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* Restrictions with slice threading also apply.
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* For best performance, the client should set thread_safe_callbacks if it
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provides a thread-safe get_buffer() callback.
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* There is one frame of delay added for every thread beyond the first one.
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Clients must be able to handle this; the pkt_dts and pkt_pts fields in
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AVFrame will work as usual.
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Restrictions on codec implementations
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==============================================
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Slice threading -
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None except that there must be something worth executing in parallel.
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Frame threading -
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* Codecs can only accept entire pictures per packet.
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* Codecs similar to ffv1, whose streams don't reset across frames,
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will not work because their bitstreams cannot be decoded in parallel.
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* The contents of buffers must not be read before ff_thread_await_progress()
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has been called on them. reget_buffer() and buffer age optimizations no longer work.
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* The contents of buffers must not be written to after ff_thread_report_progress()
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has been called on them. This includes draw_edges().
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Porting codecs to frame threading
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==============================================
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Find all context variables that are needed by the next frame. Move all
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code changing them, as well as code calling get_buffer(), up to before
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the decode process starts. Call ff_thread_finish_setup() afterwards. If
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some code can't be moved, have update_thread_context() run it in the next
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thread.
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If the codec allocates writable tables in its init(), add an init_thread_copy()
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which re-allocates them for other threads.
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Add AV_CODEC_CAP_FRAME_THREADS to the codec capabilities. There will be very little
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speed gain at this point but it should work.
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If there are inter-frame dependencies, so the codec calls
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ff_thread_report/await_progress(), set AVCodecInternal.allocate_progress. The
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frames must then be freed with ff_thread_release_buffer().
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Otherwise leave it at zero and decode directly into the user-supplied frames.
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Call ff_thread_report_progress() after some part of the current picture has decoded.
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A good place to put this is where draw_horiz_band() is called - add this if it isn't
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called anywhere, as it's useful too and the implementation is trivial when you're
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doing this. Note that draw_edges() needs to be called before reporting progress.
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Before accessing a reference frame or its MVs, call ff_thread_await_progress().
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