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• Running a 2-pass video conversion using Python's subprocess module and ffmpeg

  22 novembre 2012, par ensnare

  I'm trying to convert a bunch of videos to play on my iPad. I'm using the subprocess module, which from what I understand launches a binary in a separate process from my script. I'm not sure how to handle 2-pass encoding which requires that the first process terminate before the second begin.

  Here is my code :

  def convert(filename):
  
    extension = filename[-3:]
  
  
  
    destination_filename_720 = filename[-4:] + '-a720p' + '.mp4'
  
    destination_filename_1080 = filename[-4:] + '-a1080p' + '.mp4'
  
  
  
    p = subprocess.Popen(['ffmpeg','-i', str(filename) ,
  
                          '-acodec' , 'aac' ,
  
                          '-ab' , '160k' ,
  
                          '-ac' , '2' ,
  
                          '-vcodec' , 'libx264' ,
  
                          '-strict' , '-2' ,
  
                          '-vpre' , 'ipod640' ,
  
                          '-threads' , '8' ,
  
                          '-s' , '1280x720' ,
  
                          '-b:v' , '2000k' ,
  
                          '-pass' , '1' ,
  
                          '-y' ,
  
                          destination_filename_720])
  
  
  
    p = subprocess.Popen(['ffmpeg','-i', str(filename) ,
  
                          '-acodec' , 'aac' ,
  
                          '-ab' , '160k' ,
  
                          '-ac' , '2' ,
  
                          '-vcodec' , 'libx264' ,
  
                          '-strict' , '-2' ,
  
                          '-vpre' , 'ipod640' ,
  
                          '-threads' , '8' ,
  
                          '-s' , '1280x720' ,
  
                          '-b:v' , '2000k' ,
  
                          '-pass' , '2' ,
  
                          '-y' ,
  
                          destination_filename_720])

  As soon as the convert() function is called, both processes are spawned immediately.

  The second process fails because the first process hasn't yet finished.

  How can I fix this ? Or, is there a better way ?

• ffmpeg streaming multiple avi files as created

  2 janvier 2013, par aboredprogrammer

  Backstory :
  I have a VB.net program (that is using a much older COM object accessing a DVR) to create sequentially numbered AVI files each 15 seconds in length. A new AVI is created every 15 seconds with the most recent 15 seconds of video in it. I know the exact datetime that correlates to each file. So files may be named (20121008-133445.avi, so yyyyMMdd-hhmmss.avi).

  Question : Using ffmpeg/ffserver (preferably but I'm open), how can I create a stream such that when a person accesses it that they are presented a continuous video that starts at a position that is as recent as possible and continues to stream the avi files as they are created ?

  I don't have a problem shipping these files off to a Linux box via a samba share (or have the linux box access a share on the windows box) if Linux is more capable. I am however stuck with Windows for the actual generation of the original AVI files.

  The ultimate goal is to be able to view these streams on an iPad, but that process seems pretty well documented elsewhere.

  I found a question that reads similar to my needs but didn't seem to go anywhere : FFmpeg make mpeg2 ts without discontinuity

  Thanks in advance !

• Set background colour when converting flv to mp4 with ffmpeg

  28 août 2012, par Castles

  I'm attempting to convert flv files (with an alpha channel) that are uploaded to a server to html5 compatible formats. I've got the conversion working but the transparency is rendered as black. What I would like to do is have the ability to specify a colour.

  Is it possible to convert the video and specify the colour ?

  Alternatively, am I able to overlay the video with transparency on a still image that I generate ?

  Update
  I may of solved my own question... Here is my ffmpeg command :

  `ffmpeg -loop_input -f image2 -i background.png -r 25 -t 10 -an -level 21 -refs 2 -b 345k -bt 345k -acodec libfaac -vcodec libx264 -ac 2 -ab 96k -ar 44100 -vf "movie=input.flv, scale=370:500 [logo]; [in][logo] overlay=0:0 [out]" -y -threads 0 output.mp4`

  Which works.. I just need to generate a background image at the right dimensions on the server before converting.