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• movenc : Add a flag for indicating a discontinuous fragment

  20 novembre 2014, par Martin Storsjö

  movenc : Add a flag for indicating a discontinuous fragment
  This allows creating a later mp4 fragment without sequentially
  
  writing the earlier ones before (when called from a segmenter).
  Normally when writing a fragmented mp4 file sequentially, the
  
  first timestamps of a fragment are adjusted to match the
  
  end of the previous fragment, to make sure the timestamp is the
  
  same, even if it is calculated as the sum of previous fragment
  
  durations. (And for the first packet in a file, the offset of
  
  the first packet is written using an edit list.)
  When writing an individual mp4 fragment discontinuously like this
  
  (with potentially writing the earlier fragments separately later),
  
  there’s a risk of getting a gap in the timeline if the duration
  
  field of the last packet in the previous fragment doesn’t match up
  
  with the start time of the next fragment.
  Using this requires setting -avoid_negative_ts make_non_negative
  
  (or -avoid_negative_ts 0).
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavformat/movenc.c
  • [DH] libavformat/movenc.h

• How can I concatenate MP4 videos and exactly match this combined video to an audio track in ffmpeg ?

  17 juin 2020, par mattador

  Basically I want to combine 4 videos into a single video, then swap out the concatenated audio for another track. The audio track needs to be unaltered and sync exactly to the video.

  



  Specifically, I'm creating multipaged dynamic audio spectrograms (visualizations of a sound file) using ggplot2 and gganimate in R, which I want to combine using ffmpeg. So the original WAV is chopped up into 3 sec segments, a video is created to visualize frequency changes over time for each segment, which I want to combine into 1 video with the original audio track matched up.

  



  All of my relevant files are at github here in the vids folder : DL link here

  



  The individual dynamic spectrograms export fine (1-4.mp4 in the archive). They are each 20ms too long ; they should be exactly 3s, but otherwise great.

  



  I then use ffmpeg to concatenate them :

  



  ffmpeg -f concat -safe 0 -i "mp4Segments.txt" -codec copy -t 12 -y "(1-4)vid.mp4"


  



  but you can see the end of (1-4)vid.mp4 is getting a little off (the cursor is not all the way to the end, so I guess the video is getting cut off before the end. Not a deal-breaker, since the audio still aligns very well to the video cursor.

  



  Now, since the concatenated video introduces glitchy audio between clips, I want to take the uncut original audio and add that to the assembled video.

  



  ffmpeg -ss 0 -i "(1-4)vid.mp4" -i "origWAV.wav"  -c:v libx264 -map 0:v:0 -map 1:a:0 -c:a aac -ac 1 -b:a 192k -y -vsync 1 -t 12 "(1-4)vid+origWAV.mp4"


  



  but the audio is slightly off now, and ends even further before the end of the video. Since it's really important to align audio and video precisely for this, how can I speed up the video to fit the exact duration of the audio or otherwise fix this issue ?

  


• FFMPEG.wasm Cannot Add Album Cover To MP3 File

  5 juillet 2022, par Shaan Khan

  for a project I'm working on I'm trying to split a video into multiple audio clips whilst adding metadata for each individual track. Whilst doing this, whilst I've added most of the metadata including title & artist, I'm unable to add an album cover via FFMPEG.wasm. Whilst my command works fine with regular FFMPEG.wasm, I'm unable to get it to work via the webassembly version.

  


  I'm aware that my album cover is correctly being assigned via FS.readfile and that my command in theory should work, but I'm unable to figure out why it isn't working. Is this a FFMPEG.wasm limitation and if so, is there any workaround for this ?

  


  

  • Normal FFMPEG Command

  


  


  ffmpeg -i "song.mp3" -i albumCover.jpg -map 0:0 -map 1:0 -y -codec:a libmp3lame -ac 2 -ar 48000 -ab 320k -ss 00:00:00 -t 00:00:20 -id3v2_version 3  -metadata title="SongOne" -metadata album_artist="Artist Name" -metadata album="Youtube Name" -metadata track="1" "output.mp3"


  


  

  • FFMPEG WASM Implementation

  


  


    let commandArray = [
      "-i",
      "song.mp3",
      "-i",
      "albumCover.jpg",
      "-map",
      "0:0",
      "-map",
      "1:0",
      "-y",
      "-codec:a",
      "libmp3lame",
      "-ac",
      "2",
      "-ar",
      "48000",
      "-ab",
      "320k",
      "-ss",
      startTime.toString(),
    ];

    if (duration != "-1") {
      commandArray.push("-t", duration.toString());
    }

    commandArray.push(
      "-id3v2_version",
      "3",
      "-metadata",
      `title="${title}"`,
      "-metadata",
      `album_artist="${artist}`,
      "-metadata",
      `album="${albumInfo.name}"`,
      "-metadata",
      `track="1"`,
      `${timestamp.songName} - ${timestamp.artistName}.mp3`
    );