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• Uploading & Processing Videos in Rails app on Heroku

  8 octobre 2015, par scientiffic

  In my Rails app, users can upload videos. The videos need to get converted to mp4s to ensure they can play across browsers, and they are hosted on AWS S3.

  If the video conversion (using ffmpeg) happens quickly, the resulting mp4 is rendered directly on the page so the user can immediately view the uploaded video. Sometimes, though the conversion takes long enough that I get Heroku H12 errors (request timeout), which prevents the video preview from appearing.

  Is there a recommended workflow for dealing with processing larger files in a Rails app using Heroku ?

  The option that immediately comes to mind is processing in a background task using something like Sidekiq, but then the user doesn’t receive feedback when the upload is complete.

• avformat/mxfenc : set/force channelcount in MXF D-10

  25 juin 2014, par Gaullier Nicolas

  avformat/mxfenc : set/force channelcount in MXF D-10
  There are interoperability issues with D-10 related to the channelcount property in the generic sound essence descriptor.
  On one side, SMPTE 386M requires channel count to be 4 or 8, other values being prohibited.
  
  The most widespread value is 8, which seems straightforward as it is the actual size of the allocated structure/disk space.
  
  At the end, it appears that some vendors or workflows do require this descriptor to be 8, and otherwise just "fail".
  On the other side, at least AVID and ffmpeg do write/set the channel count to the exact number of channels really "used",
  
  usually 2 or 4, or any other value. And on the decoding side, ffmpeg (for example) make use of the channel count for probing
  
  and only expose this limited number of audio streams
  
  (which make sense but has strong impact on ffmpeg command line usage, output, and downstream workflow).
  At the end, I find it pretty usefull to simply give ffmpeg the ability to force/set the channel count to any value the user wants.
  
  (there are turnaround using complex filters, pans, amerge etc., but it is quite boring and requires the command line to be adapted to the input file properties)
  Reviewed-by : Matthieu Bouron <matthieu.bouron@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavformat/mxfenc.c

• Can I decode this audio format ?

  30 octobre 2013, par Naftuli Tzvi Kay

  I'm writing a Python program which depends on FFMPEG to decode audio into WAV format. I'd like to be able to process as many types of audio, but I need a way to quickly check if I can actually work with the uploaded file or not. I've compiled my own FFMPEG installation here.

  Specifically, I'd like to enforce logic like this in my application :

  if ffmpeg_type(file_path) is not "audio":
  
      raise Exception("Bro, that's not an audio file.")
  
  elif not ffmpeg_can_decode_audio(file_path):
  
      raise Exception("I have no way of working with this.")

  (I realize that it wouldn't be as easy as just calling these methods, I assume I'd need to parse output from a system call.)

  Is there a way that I could use the command-line ffmpeg, ffprobe, etc. to determine if a given file is an audio file and if I can decode it ?