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• Encode mjpeg files from within an iOS app

  9 mai 2017, par Ricardo Sanchez-Saez

  I’m trying to encode a video file with the mjpeg codec on iOS. Basically, I’m trying to replicate what this command does

  ffmpeg -i recording.mp4 -vsync vfr -q:v 9 recording.mjpeg

  from within an app.

  Is there an easy way to do this ?

  I’m looking at using the low level ffmpeg API to do this like in this example, but I was wondering if somebody knows of a simpler way.

  I have also access to the individual video frames in CMSampleBufferRef format, in case that makes it easier. AVAssetWriter doesn’t seem to support mjpeg, which is unfortunate, as that would make things super simple.

• How to Create video from selected images of a folder using FFMPEG ?

  20 février 2018, par Hadley V Sunny

  For the time being I am doing

  ProcessStartInfo ffmpeg = new ProcessStartInfo();
  
  ffmpeg.CreateNoWindow = false;
  
  ffmpeg.UseShellExecute = false;
  
  
  
  ffmpeg.FileName = "e:\ffmpeg\ffmpeg.exe";
  
  ffmpeg.Arguments = "for file in (D:\\Day\\*.jpg); do ffmpeg -i \"$file\" -vf fps=1/60 -q:v 3 \"D:\\images\\out.mp4\"; done;";
  
  ffmpeg.RedirectStandardOutput = true;
  
  Process x = Process.Start(ffmpeg);

  Here I’m getting exception saying system cannot find specified file.
  For time being I’m considering all the files in D :\Day*.jpg but actually I need to query individual files from a list.

  Where am I wrong in the above scenario ?

• Creating an Init file from existing non-fragmented, segmented MP4 files

  20 novembre 2018, par slhck

  I am performing chunked encodes of longer video files, where I’ve split the original file into individual sequences that I have encoded separately. These sequences are files of different length, depending on where the scene cuts appear—they may be between 2 and 5 seconds long. They all start with an I-frame and are standalone.

  My encoded sequences are all MP4s, e.g. :

  test_0000.mp4
  
  test_0001.mp4
  
  test_0002.mp4
  
  test_0003.mp4
  
  test_0004.mp4

  They all have common properties :

  $ mp4info test_0000.mp4
  
  
  
  File:
  
    major brand:      isom
  
    minor version:    200
  
    compatible brand: isom
  
    compatible brand: iso2
  
    compatible brand: mp41
  
    fast start:       no
  
  
  
  Movie:
  
    duration:   2016 ms
  
    time scale: 1000
  
    fragments:  no
  
  
  
  ...

  Now, in order to play those with a DASH player, I have to create an initialization segment and individual fragmented MP4s.

  I could generate the fragmented MP4s via mp4fragment which I run on each standalone MP4 file :

  $ mp4info test_0000.m4s
  
  File:
  
    major brand:      isom
  
    minor version:    200
  
    compatible brand: isom
  
    compatible brand: iso2
  
    compatible brand: mp41
  
    compatible brand: iso5
  
    fast start:       yes
  
  
  
  Movie:
  
    duration:   2016 ms
  
    time scale: 1000
  
    fragments:  yes
  
  
  
  ...

  But obviously, these are now not according to spec, and all contain a moov atom :

  

  What I’d need is individual media segments with only one moof and mdat box, which then require an initialization segment with only a moov box.

  How can I generate that from the existing, already encoded segments ?

  I know this appears like an XY problem. In principle, I could already segment my original file directly after encoding, and run those encodes at the same time, e.g. using ffmpeg’s dash muxer, or MP4Box, however :

  • There is almost no control over the resulting segment sizes, with respect to minimum and maximum duration
  • This approach does not parallelize

  I have also checked Bento4 ; it does not seem to offer this functionality. Neither does FFmpeg. MP4Box behaves similarly. They all assume you have one long file to start with.

  ---

  I see I could splice off the ftyp and moov boxes from these “fake fragments” in order to create an initialization segment. But I would end up with segments containing multiple moof and mdat boxes, which is not according to the specification – it only allows one fragment and media data box :

  4. Media Segments

  […] one optional Segment Type Box (styp) followed by a single Movie Fragment Box (moof) followed by one or more Media Data Boxes (mdat).

  I guess I can live with this the styp not being present.