[Live-devel] testRTSPClient does not assemble frames correctly

[Ross Finlayson]

> However, we are finding a variable number of P frames.  Sometimes you will get an I frame every 10th frame, sometimes every 16th frame, etc.
> I think what's happening is that sometimes multiple P frames are being combined into a single P frame.
> 
> This variable GOP size is a problem for a lot of decoders.
> 
> 
> So far we have tested this on 3 different RTSP sources with the same result.

What type of data is this?  MPEG-2 Elementary Stream video? H.264 Elementary Stream video?  MPEG Transport Stream (containing MPEG-2 or H.264 video)? 

Do the "3 different RTSP sources" come from servers implemented using our code (e.g., using one of our server demo applications), or using some other RTSP server implementation?

Are you seeing network packet loss (you can test this by running "openRTSP -Q" on the stream)?  If you are seeing significant packet loss, then be sure to read http://www.live555.com/liveMedia/faq.html#packet-loss

It's unlikely that our RTP receiving code is 'combining multiple P frames into a single P frame' if the source data is formatted properly according to the appropriate RTP payload format.  But if network packet loss is occurring, then the received stream will (of course!) have missing frames (including probably some missing I-frames, because they are larger and thus more susceptible to packet loss (unless they have been built as multiple 'slices')).  These lost frames will (of course!) cause video artifacts when the the video is decoded and rendered.


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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