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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.

• Capture live video from a camera on a computer and using ffmpeg

  21 juin 2013, par Devendra

  I am trying to capture live video from a camera on a computer and using ffmpeg as an encoder, send this video for live streaming to a IIS server.

  Here is what I did :

  1. Captured feed from webcam using video4linux2 and ffmpeg

  2. Installed x264 for a h.264 codec

  3. Used muxer feature in ffmpeg, as described on this link -
     http://www.ffmpeg.org/ffmpeg-formats.html#Muxers
     to generate ismv file locally
     Command -
     ffmpeg -f video4linux2 -r 25 -s 640x480 -i /dev/video0 -b:v 661k -c:v libx264 -movflags isml+frag_keyframe+empty_moov -f ismv test.ismv

  4. Now to get the complete system in place (live capture from webcam and live streaming on IIS server), I want ffmpeg to generate this ffmpeg file on a publish point. here is the command I used
     ffmpeg -f video4linux2 -r 25 -s 640x480 -i /dev/video0 -b:v 661k -c:v libx264 -movflags isml+frag_keyframe+empty_moov -f ismv http://www.MY-SERVER/PushToPublishPoint/Test.isml

  as described at this link :

  http://www.unified-streaming.com/support/documentation/content-delivery/publishing-points/
  http://www.unified-streaming.com/support/documentation/content-encoding/encoders/

  It shows some video is being generated, but I cannot see any activity at the server.

  When I use wireshark to look at the packet info, there are many packet transfers between pc and the server.

  I have kept publishing point in IDLE state, STARTING state to see if that is the problem, but no progress there as well.
  I think I am unable to establish communication with the server. Pls help.

  Any help would be appreciated.

  Thanks

• FFmpeg error - “at least one output file must be specified” windows version

  30 juin 2016, par AComputert

  I’m having a little trouble, and I feel like the solution is probably starting me in the face.
  How Can I extract mp4 from HTTP live streaming m3u8 file ? I Tried this command below :

  ffmpeg -i http://ms1.movieland.ir/marci6z9OSicn34CRRcin2y4nv6KRZvigAIBsBbBGlj2HUPZBeEOY1019Zxc6zlQrq3ZkYrW0PiM1WDbpVn2JQ2/vod/5787c62c-fb29-4ca4-a328-b7447bb83436/medialist.m3u8?rpt=%5C2016%5C6%5C5787c62c-fb29-4ca4-a328-b7447bb83436&pid=0 -c copy -bsf:a aac_adtstoasc f:\stream\dora.mp4

  When run, this yells at me that "At least one output file must be specified". I’ve been knocking me head on the wall for hours now, what am I missing ?