[FFmpeg-devel] [PATCH] af_asetnsamples: push as many frames as ready

[Nicolas George]

Le duodi 22 thermidor, an CCXX, Andrey Utkin a écrit :
> Could you please elaborate what you mean?
> Personally I don't see any possible pushing behaviour except the
> currently implemented.

Let us assume the frame size is 1000:

Version 1:

prev->asetnsamples: push 0000-2999
asetnsamples->next: push 0000-0999 (1000-2999 still in FIFO)
                    stop
prev->asetnsamples: push 3000-5999
asetnsamples->next: push 1000-1999 (2000-5999 still in FIFO)
                    stop

This version is bad, because data is accumulating in the FIFO.


Version 2:

prev->asetnsamples: push 0000-2999
asetnsamples->next: push 0000-0999
                    push 1000-1999
                    push 2000-2999
                    stop
prev->asetnsamples: push 3000-5999
asetnsamples->next: push 3000-3999 (4000-5999 still in FIFO)
                    push 4000-4999 (5000-5999 still in FIFO)
                    push 4000-4999 (FIFO empty)
                    stop

This version is acceptable: no data is accumulating. But it is not perfect,
because asetnsamples is flooding next instead of returning. The application
is stuck inside libavfilter, and during that time some soundcard buffer may
be underrunning.


Version 3:

prev->asetnsamples: push 0000-2999
asetnsamples->next: push 0000-0999 (1000-2999 still in FIFO)
                    stop
prev->asetnsamples: push 3000-5999
asetnsamples->next: push 1000-1999 (2000-2999 still in FIFO)
                    push 2000-2999 (FIFO empty)
                    push 3000-3999 (4000-5999 still in FIFO)
                    stop

In this version some data stays in the FIFO longer than strictly necessary,
but the amount is bounded by by the size of the pushes from the previous
filter.

The benefit is that before prev pushes the next batch, next has time to
request the rest of the data, at its own rhythm.


Version 2 would be implemented by the following pseudo-code:

	add_frame_to_fifo(inref);
	while (fifo_large_enough())
	    push_one_frame();

Version 3 would be implemented by the following code:

	while (fifo_large_enough())
	    push_one_frame();
	add_frame_to_fifo(inref);
	if (fifo_large_enough())
	    push_one_frame();

Regards,

-- 
  Nicolas George
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