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• Install PyAV on Windows

  16 juin 2015, par m.barz

  I got a problem building and thus setting up PyAV 32-bit on Windows 8 (x64). I tried the workflow for Windows as indicated in their documentation, but did not succeed :

  • I cross-compiled ffmpeg on Ubuntu 14.04 with the aid of a script.
  • I copied the *shared-install folder to Windows and set the PKG_CONFIG_PATH environment variable to the corresponding libs/pkgconfig path.
  • I copied the ffmpeg DLLs and its dependencies from the MinGW bin-folder to PyAV’s av folder as mentioned in PyAV’s docs.
  • I ran make build-mingw32 (where build-mingw32 is a recipe triggering python distutils like that : CFLAGS=$(CFLAGS) LDFLAGS=$(LDFLAGS) python setup.py build_ext --inplace -c mingw32)

  Finally I run into trouble with that last command. When the build process tries to create codec.pyd there is a bunch of undefined reference to _head_C_build27_cpython_PCBuild_libpython27_a errors leading gcc to fail. See cmd output below :

  

  I tried this on a fresh virtual machine running Windows 8.1 Pro having installed the MinGW toolchain including msys (I used the installer from mingw.org). I also tried the MinGW installer provided here.
  I hope someone already experienced similar issues using gcc and can help me with that !

  Thanks in advance and best regards,
  Michael

• Modifying incorrect h.264 dimension in existing video file

  11 juin 2015, par RichyJ

  After searching a lot, I’m more confused than ever !! To summarise :

  I recorded a video using my HTC One M8, using 1920x1088 resolution, and it came out fine. The next day, for some reason, in the settings I changed to 1920x1080 and the next video was weird - green bar across the top, diagonal green lines throughout and odd colour stripes. The underlying image was fine, although there seem to be some ’frame jumps’ at times. Unfortunately, this second video contained a section I would like to keep, so I’m trying to fix it...

  I’ve learned a bit about AVC/H.264, but it’s pretty confusing. Essentially, I wonder whether I can just change the ’1080’ in the file info to ’1088’ and salvage the footage - there’s no audio to worry about. I read that since 1080 is not directly divisible by 16, most encoders actually do 1088 then the player discards the remaining 8 lines at playback time. I wonder whether this is the root of the problem ? I tried to get into NALs, SPS/PPS etc, but couldn’t really fathom whether this was even relevant to my problem. A hex search didn’t even find anything that looked like the NALs given as examples elsewhere :

  Finding SPS/PPS data strings

  What does this NAL header data mean ?

  Fetching dimensions of a video

  I’ve loaded both files into a Hex editor and compared as best I can (around the moov and avcC parts), but haven’t fixed it yet. One of the single byte changes I made and saved to a new ’test’ file brought up additional info in the mediainfo program, showing that the original recording was at 1088 - this hadn’t been there before, but it still played wrongly. I found info regarding the encoding of height and width (units-1 * 16) but couldn’t work out how to use this info in practice.

  I tried ffmpeg and dumping to raw video, but couldn’t make this play at all as a yuv file.

  So, my question is, will I be able to change just one byte (or a few) in the file, to make it read as 1088 to the player, or am I looking in totally the wrong direction ?!? Is this even possible ? As I say, the actual images look intact throughout, just the colours are wrong and the lines are there, so I believe it’s something to do with YCrCb problems, but at this point, I’m lost...

  I know this isn’t specifically about programming, but the above links were all from this site, so thought it might be OK to ask here. Any help would be much appreciated !!

  I’ve recreated the conditions and done 2 short clips at 1080 and 1088 for you to see the problem but as I’m new, I can’t post them here yet. They’re on my Photobucket page if you are willing to look at them (hope this isn’t breaking the rules !!). The blueish line at the bottom is the windowsill...

  1088 still

  1080 still

• Embedding timed text metadata in MP4

  10 juin 2015, par Steve Robinson

  Is it possible to manually embed timed text metadata into MP4 files ?
  I have a TTML / SRT file with the metadata. I just need to embed the text data without doing any encoding the video / audio.

  EDIT :
  We used to do the metadata injecting using on Wowza server which we use for live streaming. What I need to do is manually inject the metadata in to prerecorded MP4 files without running the video through Wowza.

  Here is one such video file that was processed by Wowza :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'metadata-back.mp4':
  
    Metadata:
  
      major_brand     : f4v 
  
      minor_version   : 0
  
      compatible_brands: isommp42m4v 
  
      creation_time   : 2015-04-16 11:12:39
  
    Duration: 00:00:11.70, start: 0.000000, bitrate: 1373 kb/s
  
      Stream #0:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p(tv), 640x480 [SAR 1:1 DAR 4:3], 1352 kb/s, 28.60 fps, 30 tbr, 90k tbn, 60 tbc (default)
  
      Metadata:
  
        creation_time   : 2015-04-16 11:12:39
  
        handler_name    : WowzaStreamingEngine
  
        encoder         : WowzaStreamingEngine
  
      Stream #0:1(eng): Audio: speex (spex / 0x78657073), 16000 Hz, mono, s16, 17 kb/s (default)
  
      Metadata:
  
        creation_time   : 2015-04-16 11:12:39
  
        handler_name    : WowzaStreamingEngine
  
      Stream #0:2(eng): Data: none (amf0 / 0x30666D61), 0 kb/s (default)
  
      Metadata:
  
        creation_time   : 2015-04-16 11:12:39
  
        handler_name    : WowzaStreamingEngine

  Now if I run the command ffmpeg -i new-meta.mp4 -i sub.srt -c copy -c:s mov_text -movflags +faststart out.mp4 and if I run ffmpeg -i out.mp4, I get this :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'out.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf56.4.101
  
    Duration: 00:00:07.27, start: 0.000000, bitrate: 925 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1366x768 [SAR 1:1 DAR 683:384], 920 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Subtitle: mov_text (tx3g / 0x67337874), 0 kb/s (default)
  
      Metadata:
  
        handler_name    : SubtitleHandler

  Now as you can see the text is embedded with a different codec (is this the right term ?). Also I dont see an audio track as well.

  Hope my question is clear enough. I need a way to embed metadata (from srt / ttml) into an MP4 video it should be embedded in amf format (again is this the right term ?)