[gst-devel] How to keep multiple input sources in sync?

[Francis Rammeloo]

I have a pipeline that combines three incoming streams (webcam, desktop
capture, and a logo) into one movie using the videomixer plugin. I created
the pipeline in text and load it into my program with gst_parse_launch. The
pipeline description looks like this:


      desktop. ! queue
               ! ffmpegcolorspace
               ! videoscale
               ! video/x-raw-yuv,width=640,height=400
               ! videobox right=-320
               ! ffmpegcolorspace
               ! vmix.sink_0
      webcam. ! queue
              ! ffmpegcolorspace
              ! videoscale
              ! video/x-raw-yuv,width=320,height=240
              ! vmix.sink_1
      logo. ! queue
            ! jpegdec
            ! ffmpegcolorspace
            ! videoscale
            ! video/x-raw-yuv,width=320,height=160
            ! vmix.sink_2
      vmix. ! queue
            ! ffmpegcolorspace
            ! dshowvideosink
      dx9screencapsrc name="desktop"
      ksvideosrc device-name="Built-in iSight" name="webcam"
      multifilesrc name="logo" location="chrome/skin/ivpv.jpg"
      videomixer name=vmix
                 sink_0::xpos=0 sink_0::ypos=0 sink_0::zorder=0
                 sink_1::xpos=640 sink_1::ypos=0 sink_1::zorder=1
                 sink_2::xpos=640 sink_2::ypos=240 sink_2::zorder=2

The pipeline is playable, but the webcam is terribly out of sync. The
desktop capture is fine. If I leave out the desktop capture element and only
combine the webcam and the logo image then it's also fine. It seems that
only the combination of the desktop and webcam capture is problematic.

Any idea on how I should fix this?

Francis
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