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• ffmpeg sync issue when muxing audio and video

  25 août 2018, par tweecore

  I have an issue with ffmpeg. I am not a pro user so I’m on a constant trial & error mode. I would need a little help from this community that helped me countless time before.
  I downloaded separate audio and video segments of a video stream. Both audio and video were shown in the Network tab as being .m4s files, but the .m3u8 playlist gave me .ts files for both. So then I downloaded the whole audio batch and concatenated it into a single .ts file. I did the same with video, but using a .mp4 output.
  

  EDIT : When merging the audio .ts files, I encounter this issue :

  [mpegts @ 0x7f88cb805600] Non-monotonous DTS in output stream 0:0; 
  
  previous: 1077120, current: 1073280; changing to 1077121. This may 
  
  result in incorrect timestamps in the output file.

  UPDATE : Just noticed that when I examine the .ts audio file with MediaInfo, the frame rate is 41.667 fps (1152 SPF).

  So now I have two files : a working single .ts with audio and a working single .mp4 with video.
  Only when I tried to merge them, however, I noticed that audio and video resulted as out of sync.
  This is because audio has a different length from video (don’t know why, they were the same amount of segments : 750).
  Audio info :

  Input #0, mpegts, from 'output.ts':
  
  Duration: 01:14:12.11, start: 1.400000, bitrate: 434 kb/s
  
  Program 1 
  
  Metadata:
  
    service_name    : Service01
  
    service_provider: FFmpeg
  
  Stream #0:0[0x100]: Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, stereo, fltp, 384 kb/s

  I can see that for some reason, it starts at 1.4s.

  Video info :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  
  Metadata:
  
  major_brand     : isom
  
  minor_version   : 512
  
  compatible_brands: isomiso2avc1mp41
  
  encoder         : Lavf58.12.100
  
  Duration: 01:14:57.84, start: 0.000000, bitrate: 2425 kb/s
  
  Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 2423 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc (default)
  
  Metadata:
  
    handler_name    : VideoHandler

  Video and audio are synced at the beginning (somehow the 1.4 start makes sense) but audio starts drifting and goes out of sync after a while. How do I solve the issue ?

• how to convert HLS to RTMP with DISCONTINUITY tag

  21 août 2018, par bekks8

  We have software that produces concatenated HLS files. This concatenation is basically just playlist manipulation. We replace some parts of the manifest by other parts. To make the HLS valid we add a #EXT-X-DISCONTINUITY tag before and after the change :

  #EXTM3U
  
  #EXT-X-VERSION:3
  
  #EXT-X-TARGETDURATION:5
  
  #EXT-X-MEDIA-SEQUENCE:0
  
  #EXT-X-PLAYLIST-TYPE:VOD
  
  #EXTINF:4.0000,
  
  http://host/stream/1
  
  #EXT-X-DISCONTINUITY
  
  #EXTINF:4.0000,
  
  http://host/stream/2
  
  #EXTINF:4.0000,
  
  http://host/stream/3
  
  #EXTINF:4.0000,
  
  http://host/stream/4
  
  #EXTINF:4.0000,
  
  http://host/stream/5
  
  #EXTINF:4.0000,
  
  http://host/stream/6
  
  #EXTINF:0.2917,
  
  http://host/stream/7
  
  #EXT-X-DISCONTINUITY
  
  #EXTINF:4.0000,
  
  http://host/stream/8
  
  #EXT-X-ENDLIST

  In an HTML5 player above manifest will play just fine. Everything is in sync, audio and video play.

  Now, when i try and convert above to an rtmp format and stream this to a rtmp endpoint it works, but it stalls after about 4 seconds, than it continues missing 4 seconds, and runs fine after that.

  Basically, it plays part 1, skips 2, and continues with 3.

  I’ve checked the logs for ffmpeg which repeat :

  [flv @ 0x7fa696837c00] Non-monotonous DTS in output stream 0:1; previous: 3924, current: 0; changing to 3924. This may result in incorrect timestamps in the output file.
  
  [flv @ 0x7fa696837c00] Non-monotonous DTS in output stream 0:1; previous: 3924, current: 23; changing to 3924. This may result in incorrect timestamps in the output file.
  
  [flv @ 0x7fa696837c00] Non-monotonous DTS in output stream 0:1; previous: 3924, current: 46; changing to 3924. This may result in incorrect timestamps in the output file.

  After the DTS warnings ffmpeg reports that it dropped 95 frames :

  frame=  102 fps= 22 q=28.0 size=     181kB time=00:00:04.34 bitrate= 341.7kbits/s dup=0 drop=95 speed=0.958x

  This of course makes, sense, when i check with ffprobe i can see that the PTS isn’t aligned (which is expected) :

  frame|pkt_pts_time=5.316667|pkt_dts_time=5.316667|pict_type=B
  
  frame|pkt_pts_time=5.358333|pkt_dts_time=5.358333|pict_type=B
  
  frame|pkt_pts_time=5.400000|pkt_dts_time=1.400000|pict_type=P
  
  frame|pkt_pts_time=5.441667|pkt_dts_time=1.441667|pict_type=P
  
  frame|pkt_pts_time=1.483333|pkt_dts_time=1.483333|pict_type=I
  
  frame|pkt_pts_time=1.525000|pkt_dts_time=1.525000|pict_type=B
  
  frame|pkt_pts_time=1.566667|pkt_dts_time=1.566667|pict_type=B

  The 95frames, is exactly the number of frames with a PKT_PTS_TIME (and DTS) in the past.

  the ffmpeg command i use to create the RTMP stream is :

  ffmpeg -fflags +igndts -re -i http://host/manifest -c:v libx264 -force_key_frames "expr:gte(t,n_forced*2)" -c:a aac -ar 44100 -r 24 -f flv rtmp://domain/some/rtmp/endpoint

  What i’m looking for is a way to convert the HLS to a valid RTMP, without it skipping the frames with a PTS in the past. I would like it to just regenerate the PTS :
  Is there a way to tell ffmpeg to regenerate the PTS/DTS timestamps in it’s output file ?

• AccessViolationException occurred in AForge.Video.FFMPEG.dll

  4 août 2018, par Prakash M

  I have a camera class, in this class I used a timer and in its tick event I am saving video using AForge.Net’s VideoFileWriter in C++/Cli (x86, .net framework : v4.6).
  This is not supposed to happen, as this is managed code. But even if I wrap in try catch block, program crashes because of AccessViolationException. I have verified that Image is not null. Something to do with VideoFileWriter. This happens anytime between app start to 30 minutes of running.

  An unhandled exception of type ’System.AccessViolationException’
  occurred in AForge.Video.FFMPEG.dll
  Additional information : Attempted to read or write protected memory.
  This is often an indication that other memory is corrupt.

  In Visual Studio’s output I see

  Exception thrown at 0x0C4D689F (swscale-2.dll) in test.exe : 0xC0000005 : Access violation writing location 0x09F83D80.
  Exception thrown : ’System.AccessViolationException’ in
  AForge.Video.FFMPEG.dll

  code :

   private: System::Void Video_Recorder_Tick(System::Object^  sender, System::Timers::ElapsedEventArgs^  e)
  
    {
  
        Bitmap^ save = ConvertMatToBitmap(image); //function to convert opencv's Mat to .net's Bitmap        
  
        if(writer!= nullptr)
  
         writer->WriteVideoFrame(save);
  
         delete save;
  
     }
  
  
  
    VideoFileWriter ^writer = gcnew VideoFileWriter();
  
  
  
    private: Void load_VideoWriter()
  
    {
  
      writer->Open("C:/video.avi", 640, 480, 10, VideoCodec::Default);        
  
    }

  Visual Studio showed few values for writer

  BitRate 400000
  Codec Default
  FrameRate 10
  Height 480
  IsOpen true
  Width 640
  

  Let me know if anybody needs more info.
  call stack didn’t help much

  

  To my surprise no one on internet is having this issue !
  Code seems straight forward, what could possibly be the issue ?