[Libav-user] Remux RTSP stream ?

[Seungyong Kwon]

And you have to set AV_PKT_FLAG_KEY for an I-frame but not for p-frames and
filter out all p-frames until you met the first I-frame..

Regards,


2016-12-29 오전 11:32에 yoann 이(가) 쓴 글:
> At 2016-12-27 14:06:14, "yoann" <yoann at woozoom.net> wrote:
>
>     Hi everyone,
>     I am trying to remux a mp4 RTSP stream (provided by an ffserver) into a mp4 file, but I am
>     struggling to get the file set correctly. I do not want to re-encode the stream for performances
>     reasons.
>
>     Using the remuxing.c example, I met different issues :
>     - if I use the example directly, the PTS and DTS of the firsts frames are mixed up and
>     av_write_interleaved_frames gives me a "Application provided invalid, non monotonically
>     increasing dts to muxer in stream 0: 4752 >= 4752" error.
>     - if I skip a random amount of frames (I would also like to be able to start remuxing from
>     anywhere in the stream and not only from the start), it produces a file which is eventually
>     readable but analyzing it with ffprobe -show_frames, it throws me a "Missing key frame while
>     reordering index according to edit list", which is understandable, I need my first frame to be
>     an keyframe I think.
>     - If I try to use AV_PKT_FLAG_KEY to ensure my first frame is a keyframe, it does not changes
>     anything, and printing the pkt.flags field give me that almost one frame on 2 i a keyframe,
>     which is false, it is around 1 on 10 for my RTSP stream. Am I not using this flag correctly ?
>
>
>
>
> I should have precised that it is a h264 stream. And from what I understood from this thread
> : https://ffmpeg.org/pipermail/libav-user/2013-December/005997.html, AV_PKT_FLAG_KEY is directly
> read from the h264 stream and not set by libavformat and is not the relevant information, the index
> entry is.
>
> So if I want to start the remuxing into a file from any random point, what would be the easiest way
> to ensure I am starting with a keyframe ?
>
> I can try to decode the first few frames and than check AVframe->key_frame but the performances will
> be poor. Is using av_seek_frame here useful is some manner ?
>
>
>
>     Here is my modified code for remuxing.c :
>
>         // same that remuxing.c before, here is around line 130
>         i = 0;
>         int have_first_keyframe = 0;
>         while (1) {
>             AVStream *in_stream, *out_stream;
>
>             ret = av_read_frame(ifmt_ctx, &pkt);
>             if (ret < 0)
>                 break;
>
>             i++;
>             if(i <= 54){ // random number to start further in the stream
>                 av_packet_unref(&pkt);
>                 continue;
>             }
>             fprintf(stderr, "pkt.flags : %d \n", pkt.flags);
>             if(!have_first_keyframe){
>                 if((pkt.flags & AV_PKT_FLAG_KEY) == 0){
>                     // not a keyframe
>                     av_packet_unref(&pkt);
>                     continue;
>                 } else {
>                     have_first_keyframe = 1;
>                 }
>             }
>         // same that remuxing.c after except I use i = 700 to break the loop and stop remuxing
>
>     Here is what the output looks like :
>     pkt.flags : 0
>     No keyframe
>     pkt.flags : 1
>     First keyframe
>     pkt.flags : 1
>     pkt.flags : 0
>     pkt.flags : 1
>     pkt.flags : 1
>     pkt.flags : 0
>     pkt.flags : 1
>     pkt.flags : 0
>     pkt.flags : 1
>     pkt.flags : 1
>     pkt.flags : 1
>     pkt.flags : 0
>     pkt.flags : 1
>     pkt.flags : 1
>     pkt.flags : 0
>     pkt.flags : 1
>     pkt.flags : 1
>     pkt.flags : 0
>     pkt.flags : 1
>
>     Someone has any advice to record an RTSP stream ?
>     Yoann
>
>
>
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