[vlc-devel] Zero-latency VLC

Maurizio Sciglio maurizio.sciglio at gmail.com
Thu Jul 5 14:25:43 CEST 2012

Thanks Rémi. Yes indeed, that's why I wrote "virtually" zero-latency :)
At the moment my stream contains only video information so I'm not
concerned about audio synchronisation or latency and I'm willing to cut
corners to get it working only for videos at this stage.
I'm not fully familiar with VLC's codebase so it would be great if you
could provide some pointers on specific areas of the code I could start
fiddling with.


On Thu, Jul 5, 2012 at 12:29 PM, Rémi Denis-Courmont <remi at remlab.net>wrote:

> On Thu, 5 Jul 2012 10:15:17 +0100, Maurizio Sciglio
> <maurizio.sciglio at gmail.com> wrote:
> > Thanks David.
> >
> > In my case I'm using x264 with the zerolatency settings for my encoding
> > back-end.
> > Being a RTSP/RTP stream, VLC is using the Live555 demux. Can anyone
> confirm
> > whether the parameters from the SDP descriptor would affect internal
> > buffering and introduce latency? I went through the code of Live555 and
> I
> > couldn't find any obvious source of internal latency. Any suggestion? I
> > also tried decreasing the Live555's RTP packet reorder size but I
> couldn't
> > notice any difference.
> It should be obvious, but there is no such thing as zero latency in the
> real world. In particular, RTP has intrinsic latency due to finite network
> bandwidth, packetization time, and inter-packet arrival delay variance
> (a.k.a. network jitter) - all three of these factors introduce latency even
> if there is no packet reordering. Packet reordering only makes latency
> worse.
> That being said, there are also some components in VLC that do not
> properly deal with low-latency cases. For instance, the audio output
> assumes a latency of at least 40ms. To reduce VLC latency, you need to
> investigate what is failing or introducing unecessary delay and fix it.
> That means debugging and patching. I really don't think you can get stable
> playback with less than 80ms with the current code base.
> --
> Rémi Denis-Courmont
> Sent from my collocated server
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