[gst-devel] async Audio/Video

[Matthias Rolf]

Hi all,

I'm using gstreamer for realizing an audio/video-synchrony-detection 
algorithm and having the following problem:  using the following 
test-script causes audio and video to go out of sync:

gst-launch-0.10 \
    filesrc location=$1 ! queue ! decodebin2 name=dec \
    dec. ! queue ! identity check-perfect=true ! \
       videorate ! ffmpegcolorspace ! ximagesink \
    dec. ! queue ! audiorate ! \
       audioconvert ! alsasink \
    --gst-debug=videorate:3,identity:4,audiorate:4

The impact highly depends on the concrete video, but I can reproduce it 
across several test-videos. You can hear/see the asynchrony and it is 
reflected in my computation results from my orignal (very large) 
pipeline (thats my pain-point!).

My observation is: when removing the queue between filesrc and decodebin 
both streams get synchronized again. Though seeming to solve the problem 
in this special case that knowledge is not sufficient to me, since the 
reliability of my results depends on whether this effect can also impact 
in other situations.

Note: audiorate and videorate are necessary for my purpose since I have 
to compute precise timing relations between audio and video and thus 
need an absolute high-quality streams.

Does anybody have an explanation or at least a hypothesis for that 
phenomenon?

Thanks in advance,
Matthias