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• Seek in fragmented MP4

  15 novembre 2020, par Stefan Falk

  For my web-client I want the user to be able to play a track right away, without having to download the entire file. For this I am using a fragmented MP4 with the AAC audio coded (Mime-Type : audio/mp4; codecs="mp4a.40.2").

  


  This is the command that is being used in order to convert an input file to a fMP4 :

  


  ffmpeg -i /tmp/input.any \
  -f mp4 \
  -movflags faststart+separate_moof+empty_moov+default_base_moof \
  -acodec aac -b:a 256000 \
  -frag_duration 500K \
   /tmp/output.mp4


  


  If I look at this file on MP4Box.js, I see that the file is fragmented like this :

  


  ftyp
moov
moof
mdat
moof
mdat
..
moof
mdat
mfra


  


  This looks alright so far but the problem I am facing now is that it's not apparent to me how to start loading data from a specific timestamp without introducing an additional overhead. What I mean by this is that I need the exact byte offset of the first [moof][mdat] for a specific timestamp without the entire file being available.

  


  Let's say I have a file that looks like this :

  


  ftyp
moov
moof # 00:00
mdat 
moof # 00:01
mdat
moof # 00:02
mdat
moof # 00:03
mdat
mfra


  


  This file however, is not available on my server directly, it is being loaded from another service, but the client wants to request packets starting at 00:02.

  


  Is there a way to do this efficiently without me having to load the entire file from the other service to my server ?

  


  My guess would be to load [ftyp][moov] (or store at least this part on my own server) but as far as I know, the metadata stored in those boxes won't help me to find a byte-offset to the first [moof][mdat]-pair.

  


  Is this even possible or am I following the wrong approach here ?

  


• Use QT format for audio sample descriptors depending on stsd version.

  5 septembre 2018, par Justin Ruggles

  Use QT format for audio sample descriptors depending on stsd version.
  ISOBMFF does not allow AudioSampleEntryV1 in stsd version 0, so
  
  assume the descriptor format is QTFF SoundDescriptionV1. ISOBMFF does
  
  not define a version 2.
  This fixes audio decoding for some MP4 files generated with Apple
  
  tools. The additional fields present in SoundDescriptionV1/V2 need to
  
  be read in order to correctly read additional boxes that contain
  
  information required for decoding the stream.
  Fixes #7376.
  Also see : https://github.com/HandBrake/HandBrake/issues/1555
  Signed-off-by : Derek Buitenhuis <derek.buitenhuis@gmail.com>
  

  • [DH] libavformat/isom.h
  • [DH] libavformat/mov.c

• AForge.Video.FFMPEG XamlParseException

  10 février 2017, par tobloef

  I’m trying to set up a simple C# application where I want to record multiple USB webcams and save their feeds to some files. I’m using AForge.NET since this seems to be the most popular option for this sort of application. I can record video fine using the AForge.Video.VFW AVIWriter but due to a number of reasons I need to use the AForge.Video.FFMPEG VideoFileWriter. Whenever I try to use this class however, I get a System.Windows.Markup.XamlParseException with no additional information or inner exceptions apart from a little additional information which is quite useless.

  

  I have a simple code example to trigger the exception :

  using AForge.Video.FFMPEG;
  
  
  
  namespace CameraPrototype {
  
      public partial class MainWindow {
  
          public MainWindow() {
  
              InitializeComponent();
  
  
  
              VideoFileWriter videoFileWriter = new VideoFileWriter();
  
          }
  
      }
  
  }

  I’ve also googled a bit around and tried some suggestion mentioned elsewhere :

  • Checking all the boxes in Exceptions Settings, enabling breaks on all types of exceptions. I had hoped this would give me some more info when the exception was thrown, unfortunately it doesn’t change anything.
  • Copying the FFMPEG DLLs (swscale-2.dll, postproc-52.dll, etc) into the same folder as the application’s built executable (../bin/Debug/). I ’m pretty sure the exception has something to do with ffmpeg, but this particular solution isn’t working. Perhaps I’m doing something wrong here or I’m missing something for ffmpeg to work ?

  If anyone have any idea what I might be doing wrong or how I can get more information about the exception, I would really appreciate any help. Let me know if I need to post any other information. Thanks !

  Edit :
  Though it doesn’t really answer the question, I’m also open to suggestions for alternatives to AForge.NET, as long as it lets me record and save video from multiple USB webcams.