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• How to append fMP4 chunks to SourceBuffer ?

  24 octobre 2020, par Stefan Falk

  I have finally managed to create an fMP4 but now I am not able to seek or play the file depending on what I do in the file.

  


  On my backend I am taking the file and convert it to MP4 or fragmented MP4.

  


  The file gets send to the clients chunk-wise but this approach does not seem to work as it used to work on Chrome (bot not on Firefox) when using MP3.

  


  How I played MP3

  


  Say we have a 10 seconds track that is 1 MB in size which I want to start playing from second five. I want to load chunks of 1 second.

  


  Thus, I have offset = 5 / 10 * file_size and chunkSize = 1 / 10 * file_size`.

  


  With this I just started loading the MP3-file at an offset of 0.5 MB and loaded the chunks as needed where each chunk was 0.1 MB in size.

  


  This worked because before actually playing the file, I loaded the first bytes of the file and appended it to the SourceBuffer as well s.t. it was able to load the meta-information of the file. However, this approach is just not working for fMP4.

  


  What I tried with fMP4

  


  So, I have been converting MP3 to fMP4 with the MP3-approach ..

  


  .. using +dash (can play but not seek)

  


  ffmpeg -i input.mp3 -acodec aac -b:a 256k -f mp4 -movflags +dash output.mp4


  


  .. using frag_keyframe+empty_moov (cannot play on Chrome)

  


  ffmpeg -i input.mp3 -acodec aac -b:a 256k -f mp4 -movflags frag_keyframe+empty_moov output.mp4


  


  On the client the chunks get appended to a SourceBuffer (as explained above) after creating it with the Mime-Type audio/mp4; codecs="mp4a.40.2" :

  


  this.sourceBuffer = this.mediaSource
                        .addSourceBuffer('audio/mp4; codecs="mp4a.40.2"');


  


  and

  


  private appendSegment = (chunk) => {
  try {
    this.sourceBuffer.appendBuffer(chunk);
  } catch {
    return;
  }
}


  


  The problem is that I can only play the +dash converted file if I start reading it from the start and continue adding chunks.

  


  However, if I start reading the file from further down, the audio gets never played.

  


  playTrack(track, 0.0);  // Start at second 0 works
playTrack(track, 10.0); // Start at second 10 does not work


  


• ffmpeg single quote in drawtext

  10 novembre 2015, par dotsam

  I haven’t been able to get ffmpeg’s drawtext video filter to draw apostrophes/single quotes when they are in drawtext’s "text=" parameter, even when I escape them. Double quotes work fine, and apostrophes in text loaded from a file (e.g. textfile="example.txt") work fine. Is this a bug ?

  e.g.

  ffmpeg -i test.mpg -vf drawtext="apostrophes don't print" ...
  
  ffmpeg -i test.mpg -vf drawtext="even when they\'re escaped" ...

• ffmpeg single quote in drawtext

  9 décembre 2023, par dotsam

  I haven't been able to get ffmpeg's drawtext video filter to draw apostrophes/single quotes when they are in drawtext's "text=" parameter, even when I escape them. Double quotes work fine, and apostrophes in text loaded from a file (e.g. textfile="example.txt") work fine. Is this a bug ?

  



  e.g.

  



  ffmpeg -i test.mpg -vf drawtext="apostrophes don't print" ...
ffmpeg -i test.mpg -vf drawtext="even when they\'re escaped" ...