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

[Troy Gardner]

Anybody ever figure out a solution on this?


On Thu, Jun 6, 2013 at 11:47 PM, Star Brilliant <b13253 at gmail.com> wrote:

> > 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
> > ffg4.mkv
> >
> > 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
> > seconds
> > http://66.220.0.170/XFG4.mkv
> >
> > 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.
> > flashsrv http://66.220.0.170/out.mov
> >
> >
> > 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
> > --enable-version3
>
>
> I have been experiencng this problem as well. After it stalls, the video
> and
> audio lost sync. However I noticed that my HDD LED flashes when the video
> stalls.
> I think that perhaps Linux kernel is trying to write buffered data to HDD,
> which
> caused delay.
> I wonder if there is a way to switch to write-through mode.
>
>