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• ffmpeg concat drops audio frames

  5 octobre 2017, par Shaun

  I have an mp4 file and I want to take two sequential sections of the video out and render them as individual files, later recombining them back into the original video. For instance, with my video video.mp4, I can run

  ffmpeg -i video.mp4 -ss 56 -t 4 out1.mp4
  
  ffmpeg -i video.mp4 -ss 60 -t 4 out2.mp4

  creating out1.mp4 which contains 00:00:56 to 00:01:00 of video.mp4, and out2.mp4 which contains 00:01:00 to 00:01:04. However, later I want to be able to recombine them again quickly (i.e., without reencoding), so I use the concat demuxer,

  ffmpeg -f concat -safe 0 -i files.txt -c copy concat.mp4

  where files.txt contains

  file out1.mp4
  
  file out2.mp4

  which theoretically should give me back 00:00:56 to 00:01:04 of video.mp4, however there are always dropped audio frames where the concatenation occurs, creating a very unpleasant sound artifact, an audio blip, if you will.

  

  I have tried using async and -af apad on initially creating the two sections of the video but I am still faced with the same problem, and have not found the solution elsewhere. I have experienced this issue in multiple different use cases, so hopefully this simple example will shed some light on the real problem.

• displaying a baseline h264 frames stream in browsers

  6 août 2021, par Thabet Sabha

  So, I have a server that receives a live rtsp stream then generates baseline h264 frames using ffmpeg, which then are sent via an rtcDataChannel to browser, and while the frames arrive as intended, I can't figure out a way to display them on my html5 videoElement,
here is a simplified version of my current approach :

  


  const remoteStream = new MediaSource();&#xA;myVideoElement.src = window.URL.createObjectURL(remoteStream);&#xA;&#xA;// called when remoteStream.readyState === "open"&#xA;let sourceBuffer = remoteStream.addSourceBuffer(&#x27;video/mp4; codecs="avc1.4d002a"&#x27;);&#xA;&#xA;// this gets called when ever a new frame is received from the webrtc data channel.&#xA;function onFrame(frame) {&#xA;      sourceBuffer.appendBuffer(new Uint8Array(frame));&#xA;&#xA;      /*&#xA;      console.log(frame) ==> <buffer 00="00" 01="01" 41="41" 9b="9b" a0="a0" 22="22" 80="80" a5="a5" d7="d7" 42="42" ea="ea" 34="34" 14="14" 85="85" ba="ba" bc="bc" 1b="1b" f2="f2" 71="71" 0d="0d" 8b="8b" e1="e1" 3c="3c" 52="52" d5="d5" 8c="8c" ef="ef" c1="c1" 89="89" 10="10" c5="c5" 05="05" 78="78" ee="ee" 1d="1d" 03="03" 8d="8d" 2896="2896" more="more" bytes="bytes">&#xA;      */&#xA;}&#xA;</buffer>

  


  ffmpeg options :

  


  [
    "-rtsp_transport", "tcp",
    "-i", `${rtspCamURL}`,  
    "-framerate", "15",
    "-c:v", "libx264",
    "-vprofile", "baseline",
    "-b:v", "600k",
    "-bufsize", "600k",
    "-pix_fmt", "yuv420p",
    '-tune', 'zerolatency',
    "-preset", "ultrafast",
    "-f", "rawvideo",
    '-'
]; 


  


  ffmpeg stream is then split using NAL delimiter (to generate individual frames) then each frame is sent via the data channel like so :
Buffer.concat([nalDelimiter, frame]).

  


  I am not sure if i'm missing something as i'm not getting any helpful errors due to the remoteSource closing as soon as the first frame arrives for some reason.

  


  or does the media source just not support raw h264 frames, and if so is there a workaround to solve this issue ? (even if it has to do with changing the ffmpeg params.

  


• Bash : sort find results using part of a filename

  13 novembre 2015, par utt50

  I have 3 webcams set up in a building, uploading still images to a webserver. I’m using ffmpeg to encode the jpgs to mp4 video.

  The directories are set up like this :

  Cam1/201504
  
  Cam1/201505
  
  Cam2/201504
  
  Cam2/201505
  
  Cam3/201504
  
  Cam3/201505

  I’m using the following bash loop/ffmpeg parameters to make one video per camera, per year. This works well so far (well... except that my SSD is rapidly degrading in performance - too many simultaneous read/write operations ?) :

  find Cam2/2013* -name "*.jpg" -print0 | xargs -0 cat | ffmpeg -f image2pipe -framerate 30 -vcodec mjpeg -i - -vcodec libx264 -profile:v baseline -level 3.0 -movflags +faststart -crf 19 -pix_fmt yuv420p -r 30 "Cam2-2013-30fps-19crf.mp4"

  The individual files are named like this (confusing ffmpeg’s built-in file sequencer) :

  Cam1_2015052413543201.jpg
  
  Cam1_2015052413544601.jpg
  
  Cam2_2015052413032601.jpg
  
  Cam2_2015052413544901.jpg

  I now need to create one video for an entire year across all 3 cameras, ordered by timestamp. To accomplish this, I need to sort the find results by the segment of the filename after the underscore.

  What do I pipe the find output to to accomplish this ? For example, the files above would be ordered like this :

  Cam2_2015052413032601.jpg
  
  Cam1_2015052413543201.jpg
  
  Cam1_2015052413544601.jpg
  
  Cam2_2015052413544901.jpg

  Any help is very much appreciated !