[FFmpeg-user] Understanding Latency Delays in FFmpeg

Carl Eugen Hoyos cehoyos at ag.or.at
Sat Sep 26 10:02:22 CEST 2015

Michael Casadevall <mcasadevall <at> ubuntu.com> writes:

> I'm currently working on building a low-latency screen 
> capture application using FFmpeg, and VP8.

I wonder if VP8 may be the encoder with the 
highest latency available.

>  3. x11grab uses the MIT-SHM extension to grab the 
> raw RGB data from X11. This has to be transcoded 
> to YUV for almost any encoder to work (x264rgb 
> appears to be an exception).

There should be multiple encoders encoding rgb, the 
may not be ideal to stream though.

>  - Is it possible to get better performance from x11grab?

Please test x11grab with the following configure options 
(and report back):
--enable-gpl --enable-x11grab --disable-libxcb

> As best I can tell, most of the latency appears to 
> becoming from having to transcode from RGB to YUV 
> formats internally within FFmpeg

I believe it is possible to make the scaling filter 
multithreaded (using slices) but it wasn't done yet.

Carl Eugen

More information about the ffmpeg-user mailing list