[vlc-devel] [WIP PATCH] audiotrack: improve perfs, make it asynchronous

Rémi Denis-Courmont remi at remlab.net
Sat Feb 14 17:49:16 CET 2015

Le vendredi 13 février 2015, 19:16:51 Thomas Guillem a écrit :
> And this latency of audio filters can cause the video frame drop I got ?

Of course not. Only the audio filter controls and audio output controls 
(volume, mute, device change) should be affected by a sleeping audio output.

Problems with video would point to a bug upstream, probably in the ES output 
buffering. It also reportedly affects ALSA and WASAPI on some systems (never 
reproducible for me).

> Ok, I did a test on my desktop, I have 400ms of delay with PulseAudio.

That´s not much. I can trivially get to 1999ms with --file-caching=3000.

> For me, having 1600ms of delay, on the few devices I tested, is to close
> to the 2000ms limit.

> So, maybe there is a right balance between queuing all buffers and just
> one.

The right balance is to queue all buffers that *can* be queued downstream of 
VLC, which improves robustness against stutter and potentially power 
management. Queueing inside VLC has only disadvantages.

> I tried having Play() waiting when there is more than 15 buffers
> queued. With that I have around 500ms of latency and no more frame drop
> or audio drift.

IIRC, WMA can have 1 seconds blocks, so I doubt that assuming 500ms latency is 
a good idea. Also some hardware outputs may have high inherent latency - 
especially the wireless or remote kinds.

Rémi Denis-Courmont

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