Streaming Video On Lossy Network

Question

Currently I have a GStreamer stream being sent over a wireless network. I have a hardware encoder that coverts raw, uncompressed video into a MPEG2 Transport Stream with h.264 encoding. From there, I pass the data to a GStreamer pipeline that sends the stream out over RTP. Everything works and I'm seeing video, however I was wondering if there was a way to limit the effects of packet loss by tuning certain parameters on the encoder.

The two main parameters I'm looking at are the GOP Size and the I frame rate. Both are summarized in the documentation for the encoder (a Sensoray 2253) as follows:

V4L2_CID_MPEG_VIDEO_GOP_SIZE: Integer range 0 to 30. The default setting of 0 means to use the codec default GOP size. Capture only.

V4L2_CID_MPEG_VIDEO_H264_I_PERIOD: Integer range 0 to 100. Only for H.264 encoding. Default setting of 0 will encode first frame as IDR only, otherwise encode IDR at first frame of every Nth GOP.

Basically, I'm trying to give the decoder as good of a chance as possible to create a smooth video playback, even given the fact that the network may drop packets. Will increasing the I frame rate do this? Namely, since the I frame doesn't have data relative to previous or future packets, will sending the "full" image help? What would be the "ideal" setting for the two above parameters given the fact that the data is being sent across a lossy network? Note that I can accept a slight (~10%) increase in bandwidth if it means the video is smoother than it is now.

I also understand that this is highly decoder dependent, so for the sake of argument let's say that my main decoder on the client side is VLC.

Thanks in advance for all the help.

Answer 1

Increasing the number of I-Frames will help the decoder recover quicker. You may also want to look at limiting the bandwidth of the stream since its going to be more likely to get the data through. You'll need to watch the data size though because your video quality can suffer greatly since I-Frames are considerably larger than P or B frames and the encoder will continue to target the specified bitrate.

If you had some control over playback (even locally capturing the stream and retransmitting to VLC) you could add FEC which would correct lost packets.