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* commit 'def97856de6021965db86c25a732d78689bd6bb0': 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>
71 lines
3.0 KiB
Plaintext
71 lines
3.0 KiB
Plaintext
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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