[FFmpeg-user] x11grab video stalls every 30 seconds in screencapture

Troy Gardner troy at troyworks.com
Tue Jun 26 15:49:24 CEST 2012

We are using latest ffmpeg, for screencapture in the cloud.

We are seeing odd dropped frame stalls in video capture every 30 seconds
for about 1-2 seconds in duration.
Audio is captured without stalls, and  Audio Video sync is perfectly fine
despite stalls.

Hoping someone had ideas, this is driving us nuts and there's nothing
obvious to explain it.

This is the capture setting we are using.
ffmpeg -f alsa -ac 2 -i pulse -f x11grab -r 30 -s 1024x768 -i :0.0  -acodec
libvorbis -ar 44100 -vcodec libx264 -preset ultrafast -gp 0 -threads 0

This is the a drop frame test case capture  with lossless x264 that shows
dropped frames around 25-26 and significant stall errors at 30 and 60

We get this trying different options, like keyframes.

This is the output  with flashsrv, which shows  similar pause around 23 and
53 seconds, and indicates it's not a libx264 specific issue.

This is running on an instance with 16 vcpu + 16gb ram, on the Amazon AWS
 there is no noticeable background process that we can see at least that
would explaing
and happens regardless if it's debian, or ubuntu.

This is the version of ffmpeg.
ffmpeg version 0.11.1 Copyright (c) 2000-2012 the FFmpeg developers
  built on Jun 26 2012 12:42:06 with gcc 4.7.1
  configuration: --arch=x86_64 --enable-avfilter --enable-vdpau
--enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex
--enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib
--disable-stripping --enable-gpl --enable-postproc --enable-swscale
--enable-x11grab --enable-libdc1394 --enable-shared --disable-static
--enable-libx264 --enable-libvpx --enable-libmp3lame --enable-libfaac
--enable-nonfree --enable-libopencore-amrwb --enable-libopencore-amrnb

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