[FFmpeg-devel] [PATCH 1/7] Revert "Revert "lavfi/buffersrc: push the frame deeper if requested.""

Nicolas George george at nsup.org
Tue Oct 17 21:12:48 EEST 2017

Le sextidi 26 vendémiaire, an CCXXVI, Tobias Rapp a écrit :
> This commit seems to break transcoding of some input files on machines with
> a lot of CPU cores. See attached script that reproduces the problem
> ("-threads 32" is used to simulate the situation of a multi-core CPU).
> Sorry for noticing late but it took me some time to track down the problem
> and git bisecting it. The issue seems to be triggered by the high number of
> audio packets in the input file (~375 packets per second). Input files that
> have a lower audio packet rate work fine.

Thanks for reporting. I fear this will be tricky to debug.

I think the change you  have tracked cannot be the cause of the issue,
since it does not touch anything related to threading.

What this change does, on the other hand, is increase the efficiency of
the scheduling in lavfi. That can cause more work for filters that do
use threading, and reveal a race condition there.

I do not have access to a 32-core system. Can the problem be reproduced
with your script with just "-threads 32" without such a system? How
ofter does it manifest?


  Nicolas George
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