Getting artifacts when trying to read video stream from YouTube

Question

I'm trying to read the video frames from the RTSP stream that I get from YouTube. Here is the link for my test video:

rtsp://v8.cache5.c.youtube.com/CiILENy73wIaGQkJlrXMiAG8BxMYDSANFEgGUgZ2aWRlb3MM/0/0/0/video.3gp

If I'm reading frames from the local file - everything is fine, but when read them from a stream I get nothing but lots of artifacts. I've googled around and found out that there might be a problem with UDP packets and switching to TCP may help but I really can't find where it is possible to change this.

Here is the function for reading a frame:

bool nextFrame(AVFormatContext *pFormatCtx, AVCodecContext *pCodecCtx, int videoStream, AVFrame *pFrame) {  AVPacket packet;
    int frameFinished = 0;

    while( !frameFinished && av_read_frame(pFormatCtx, &packet) >= 0 ) {
        // Is this a packet from the video stream?
        if( packet.stream_index == videoStream ) {
            // Decode video frame
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
        }

        // Free the packet that was allocated by av_read_frame
        av_free_packet(&packet);    
       }    
       return frameFinished!=0;  
}

I'm also getting lots of error messages in my log:

[h263 @ 0x7804c00] warning: first frame is no keyframe
[h263 @ 0x7804c00] illegal ac vlc code at 6x1
[h263 @ 0x7804c00] Error at MB: 18
[h263 @ 0x7804c00] concealing 99 DC, 99 AC, 99 MV errors
[h263 @ 0x7804c00] I cbpy damaged at 10 4
[h263 @ 0x7804c00] Error at MB: 58
[h263 @ 0x7804c00] concealing 99 DC, 99 AC, 99 MV errors
[h263 @ 0x7804c00] I cbpy damaged at 6 6
[h263 @ 0x7804c00] Error at MB: 78
[h263 @ 0x7804c00] concealing 76 DC, 76 AC, 76 MV errors
[h263 @ 0x7804c00] I cbpy damaged at 5 5
[h263 @ 0x7804c00] Error at MB: 65
[h263 @ 0x7804c00] concealing 88 DC, 88 AC, 88 MV errors
[h263 @ 0x7804c00] illegal ac vlc code at 7x5
[h263 @ 0x7804c00] Error at MB: 67
[h263 @ 0x7804c00] concealing 86 DC, 86 AC, 86 MV errors

...and so on

edit: this is 99.9% a UDP-TCP problem. I've found this link:

rtsp://195.200.199.8/mpeg4/media.amp

This is some test camera available online. It streams with artifacts. However if it has get parameter 'tcp' and if I use this

rtsp://195.200.199.8/mpeg4/media.amp?tcp

everything works without artifacts.

So to correct my question: is there any way to force YouTube or ffmpeg to use TCP ?

Answer 1

the transport protocol is a property of the IP socket you request. as such, you can have the same url (and ip:port) on both TCP and UDP transports. This means that its up to the client to open a TCP port rather than a UDP port.

This it is selected when you create your socket.

sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)

or

sock = socket(PF_INET, SOCK_STREAM, IPPROTO_UDP)

Now, I have no clue where ffmpeg does this, but surely the above can give you a clue on how to find out.