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• Extracting metadata from incomplete video files

  17 juillet 2013, par npgall

  Can anyone tell me where metadata is stored in common video file formats ? And if it would be located towards the start of the file, or scattered throughout.

  I'm working with a remote object store containing a lot of video files and I want to extract metadata, in particular video duration and video dimensions from those files, without streaming the entire file contents to the local machine.

  I'm hoping that this metadata will be stored in the first X bytes of files, and so I can just fetch a byte range starting at the beginning instead of the whole file, passing this partial file data to ffprobe.

  For testing purposes I created a 22MB MP4 file, and used the following command to supply only the first 1MB of data to ffprobe :

  head -c1024K '2013-07-04 12.20.07.mp4' | ffprobe -

  It prints :

  avprobe version 0.8.6-4:0.8.6-0ubuntu0.12.04.1, Copyright (c) 2007-2013 the Libav developers
  
    built on Apr  2 2013 17:02:36 with gcc 4.6.3
  
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0x1a6b7a0] stream 0, offset 0x10beab: partial file
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'pipe:':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 0
  
      compatible_brands: isom3gp4
  
      creation_time   : 1947-07-04 11:20:07
  
    Duration: 00:00:09.84, start: 0.000000, bitrate: N/A
  
      Stream #0.0(eng): Video: h264 (High), yuv420p, 1920x1080, 20028 kb/s, PAR 65536:65536 DAR 16:9, 29.99 fps, 30 tbr, 90k tbn, 180k tbc
  
      Metadata:
  
        creation_time   : 1947-07-04 11:20:07
  
      Stream #0.1(eng): Audio: aac, 48000 Hz, stereo, s16, 189 kb/s
  
      Metadata:
  
        creation_time   : 1947-07-04 11:20:07

  So I see the first 1MB was enough to extract video duration 9.84 seconds and video dimensions 1920x1080, even though ffprobe printed the warning about detecting a partial file. If I supply less than 1MB, it fails completely.

  Would this approach work for other common video file formats to reliably extract metadata, or do any common formats scatter metadata throughout the file ?

  I'm aware of the concept of container formats and that various codecs may be used represent the audio/video data inside those containers. I'm not familiar with the details though. So I guess the question may apply to common combinations of containers + codecs ? Thanks in advance.

• How to get stream info from opened file in ffmpeg ?

  31 mai 2013, par Srv19

  I am trying to read video file using ffmpeg. I had working code that corresponded to somewhat old version of it, and started to try and upgrade to latest build version, exchanging all those deprecated functions for their actual analogues.

  However i have run into a problem. No streams seem to be retrieved and the load of video stops dead in tracks.

  here is the code i am using :

     // Open video file
  
     if(avformat_open_input(&pFormatCtx, filename.toStdString().c_str(), NULL, NULL)!=0)
  
         return FILE_NOT_OPENED; // Couldn't open file
  
  
  
     // Retrieve stream information
  
     if(avformat_find_stream_info(pFormatCtx,NULL)<0)
  
         return NO_STREAM_INFO; // Couldn't find stream information
  
  
  
     // Dump information about file onto standard error
  
     av_dump_format(pFormatCtx, 0, filename.toStdString().c_str(), false);
  
  
  
     // Find the first video stream
  
     videoStream=-1;
  
     for(unsigned i=0; inb_streams; i++)
  
         if(pFormatCtx->streams[i]->codec->codec_type==ffmpeg::AVMEDIA_TYPE_VIDEO)
  
         {
  
             videoStream=i;
  
             break;
  
         }
  
     if(videoStream==-1)
  
         return OTHER; // Didn't find a video stream
  
  
  
     // Get a pointer to the codec context for the video stream
  
     pCodecCtx=pFormatCtx->streams[videoStream]->codec;
  
  
  
     // Find the decoder for the video stream
  
     pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
  
     if(pCodec==NULL)
  
         return CODEC_NOT_FOUND; // Codec not found
  
  
  
     // Open codec
  
     if(avcodec_open2(pCodecCtx, pCodec,NULL)<0)
  
         return CODEC_NOT_OPENED; // Could not open codec

  The problem arises in the cycle through video streams in ffmpeg::AVFormatContext *pFormatCtx. nb_streams field is 0, and i never actually enter the cycle, and codec is not loaded etc. Strange thing is, av_dump_format gives following output :

  License: GPL version 3 or later
  
  AVCodec version 3606372
  
  AVFormat configuration: --disable-static --enable-shared --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetype --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib
  
  [asf @ 004e9540] Stream #0: not enough frames to estimate rate; consider increasing probesize
  
  Input #0, asf, from 'C:/Users/Public/Videos/Sample Videos/Wildlife.wmv':
  
    Metadata:
  
      SfOriginalFPS   : 299700
  
      WMFSDKVersion   : 11.0.6001.7000
  
      WMFSDKNeeded    : 0.0.0.0000
  
      comment         : Footage: Small World Productions, Inc; Tourism New Zealand | Producer: Gary F. Spradling | Music: Steve Ball
  
      title           : Wildlife in HD
  
      copyright       : В© 2008 Microsoft Corporation
  
      IsVBR           : 0
  
      DeviceConformanceTemplate: AP@L3
  
    Duration: 00:00:30.09, start: 0.000000, bitrate: 6977 kb/s
  
      Stream #0:0(eng): Audio: wmav2 (a[1][0][0] / 0x0161), 44100 Hz, 2 channels, fltp, 192 kb/s
  
      Stream #0:1(eng): Video: vc1 (Advanced) (WVC1 / 0x31435657), yuv420p, 1280x720, 5942 kb/s, 29.97 tbr, 1k tbn, 1k tbc

  and there are 2 streams, clear as day.

  I am utterly baffled. Please help.

• iPhone - IMA WAV ADPCM audio stream for iOS

  21 mai 2013, par Siriss

  I am trying to write an app for a school project that will play a video stream of the lab. They use Foscam cameras, and from what I understand they only stream audio in FFMPEG and VLC (a wrapper of FFMPEG and others, correct ?). I can play the video stream in a UIWebView just fine, but I can't figure out how to get audio to work. I have read a bunch of post on here about the different audio stream options, but none support this format. I have also looked into VLCKit, but that seems to only work in OS X, not iOS.

  Is there a Framework, or Kit that can stream IMA WAV ADPCM audio from a VLC/FFMPEG file, or does someone know of a better way to get audio from a Foscam ?

  EDIT - I know more about the stream and I have tried a few things. I tried AVPlayer, but discovered Audio FIle Stream and Audio Queue Services but can't find a good tutorial.

  I also found THIS site, and tried the project with my stream and it did not work.