mirror of
https://github.com/nyanmisaka/ffmpeg-rockchip.git
synced 2025-10-30 04:02:04 +08:00
66 lines
2.7 KiB
Plaintext
66 lines
2.7 KiB
Plaintext
FFmpeg multithreading methods
|
|
==============================================
|
|
|
|
FFmpeg provides two methods for multithreading codecs.
|
|
|
|
Slice threading decodes multiple parts of a frame at the same time, using
|
|
AVCodecContext execute() and execute2().
|
|
|
|
Frame threading decodes multiple frames at the same time.
|
|
It accepts N future frames and delays decoded pictures by N-1 frames.
|
|
The later frames are decoded in separate threads while the user is
|
|
displaying the current one.
|
|
|
|
Restrictions on clients
|
|
==============================================
|
|
|
|
Slice threading -
|
|
* The client's draw_horiz_band() must be thread-safe according to the comment
|
|
in avcodec.h.
|
|
|
|
Frame threading -
|
|
* Restrictions with slice threading also apply.
|
|
* For best performance, the client should set thread_safe_callbacks if it
|
|
provides a thread-safe get_buffer() callback.
|
|
* There is one frame of delay added for every thread beyond the first one.
|
|
Clients must be able to handle this; the pkt_dts and pkt_pts fields in
|
|
AVFrame will work as usual.
|
|
|
|
Restrictions on codec implementations
|
|
==============================================
|
|
|
|
Slice threading -
|
|
None except that there must be something worth executing in parallel.
|
|
|
|
Frame threading -
|
|
* Codecs can only accept entire pictures per packet.
|
|
* Codecs similar to ffv1, whose streams don't reset across frames,
|
|
will not work because their bitstreams cannot be decoded in parallel.
|
|
|
|
* The contents of buffers must not be read before ff_thread_await_progress()
|
|
has been called on them. reget_buffer() and buffer age optimizations no longer work.
|
|
* The contents of buffers must not be written to after ff_thread_report_progress()
|
|
has been called on them. This includes draw_edges().
|
|
|
|
Porting codecs to frame threading
|
|
==============================================
|
|
|
|
Find all context variables that are needed by the next frame. Move all
|
|
code changing them, as well as code calling get_buffer(), up to before
|
|
the decode process starts. Call ff_thread_finish_setup() afterwards. If
|
|
some code can't be moved, have update_thread_context() run it in the next
|
|
thread.
|
|
|
|
If the codec allocates writable tables in its init(), add an init_thread_copy()
|
|
which re-allocates them for other threads.
|
|
|
|
Add CODEC_CAP_FRAME_THREADS to the codec capabilities. There will be very little
|
|
speed gain at this point but it should work.
|
|
|
|
Call ff_thread_report_progress() after some part of the current picture has decoded.
|
|
A good place to put this is where draw_horiz_band() is called - add this if it isn't
|
|
called anywhere, as it's useful too and the implementation is trivial when you're
|
|
doing this. Note that draw_edges() needs to be called before reporting progress.
|
|
|
|
Before accessing a reference frame or its MVs, call ff_thread_await_progress().
|