Adjusting attributes of v4l2src and vp8enc elements for video conferencing


Video conferencing is real time in nature. The default encoding parameters of vp8enc element of GStreamer are not always appropriate. Let us start with the following pipeline

gst-launch v4l2src ! video/x-raw-rgb,width=320,height=240 ! ffmpegcolorspace ! vp8enc ! vp8dec ! ffmpegcolorspace ! ximagesink sync=false

The CPU usage, on a PandaBoard with Ubuntu 11.04, is close to 100% (since there are 2 cores, that translates to 50%).

Now, modify the pipeline as follows

gst-launch v4l2src decimate=3 ! video/x-raw-rgb,width=320,height=240 ! ffmpegcolorspace ! vp8enc speed=2 max-latency=2 quality=5.0 max-keyframe-distance=3 threads=5 ! vp8dec ! ffmpegcolorspace ! ximagesink sync=false

Note the decimate attribute of the v4l2src element, and the attributes speed, max-latency, max-keyframe-distance, threads and quality of the vp8enc element. With these changes the CPU usage drops to 40% and the video playback is more real time.

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