FFmpeg Concat artefact between bribes

Question

I use FFmpeg to concat 3 mp4 video bribes.

FFbrope show all bribes start with a keyframes and play very well in VLC.

When playing the final video file some artefact appears when a bribe start :

ffmpeg.exe -f concat -i video_bribes.list -codec:v copy -acodec none -movflags faststart -y v_2.mp4

I tried differents options in the concat command line to re encode but artefact are still here.

What can i do to avoid this grey artefact between bribes ?

Thanks.

Answer 1

I finaly found what was going on !

The problem was at the encoding of the original video chunks.

In my encoding loop i was using this code :

    //-- PTS
    av_packet_rescale_ts(&pkt_video, m_c->time_base, m_video_st->time_base);

    if(m_frame->key_frame)
        pkt_video.flags |= AV_PKT_FLAG_KEY;

    //Write the compressed frame to the media file.
    ret = av_interleaved_write_frame(m_oc, &pkt_video);

And when i remove these two lines :

    if(m_frame->key_frame)
        pkt_video.flags |= AV_PKT_FLAG_KEY;

Everything is fine. Moreover, now i do not see the grey nor at the start of the video, nor between my chunks.

I do not understand because i'm sure that i see these lines in the FFmpeg examples... !

Does anyone can explain me whats the purpose of this AV_PKT_FLAG_KEY; ?

Thanks for your time.