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• Pipe raw audio from mp4 using ffmpeg

  24 février 2015, par user1447257

  I have following class, that enables to read audio frames per video frame :

  class AudioAcquisition :
  ’’’
  This component returns an audio signal per video frame.
  ’’’

  def __init__(self, video_filename, bufsize=10**8):
  
      '''
  
      Parameters:
  
      -----------
  
  
  
      video_filename : String of the location of video file.
  
      '''
  
  
  
      # Read info from video using ffmpeg
  
      cmd = ["ffmpeg", \
  
          '-i', video_filename]
  
      info_pipe = subprocess.Popen(cmd, stdout=subprocess.PIPE, \
  
              stderr=subprocess.PIPE)
  
      _, err = info_pipe.communicate()
  
  
  
      self.__audio_fps = int(re.search('Stream[^\n]*Audio:[^\n]*, (\d*) Hz', err).group(1))
  
      self.__video_fps = int(re.search('Stream[^\n]*Video:[^\n]*, (\d*) fps', err).group(1))
  
  
  
      # Open audio using ffmpeg
  
      cmd = ['ffmpeg', \
  
          '-loglevel', 'quiet', \
  
          '-i', video_filename, \
  
          '-vn', \
  
          '-f', 's16le', \
  
          '-acodec', 'pcm_s16le', \
  
          '-ac', '1', \
  
          '-']
  
      print " ".join(cmd)
  
      self.__pipe = subprocess.Popen(cmd, stdout=subprocess.PIPE, \
  
          stderr=subprocess.STDOUT)
  
  
  
  def run(self):
  
      '''
  
      Yields:
  
      -------
  
  
  
      An audio signal per video frame.
  
      '''
  
  
  
      while (True):
  
          try:
  
              size = int(2 * self.__audio_fps / self.__video_fps)
  
              data = self.__pipe.stdout.read(size)
  
              if (len(data) < size):
  
                  break
  
              yield numpy.fromstring(data, dtype="int16")
  
          except IOError as e:
  
              print('Error encoutered while reading audio via ffmpeg: ' \
  
                  + str(e))
  
              break

  This somehow does not work properly, as the audio is dumped out with some noise frames at about 20s and repetitively occuring more often at later timestamps.

  Do you guys have any suggestions what I am missing in calling ffmpeg ?

  Thanks !

• Using Pipe for input and output on FFMPEG ?

  2 mars 2015, par Sugrue

  I want to use ffmpeg to convert video packets to mjpeg, and ideally, I want to pipe in the gob packet and receive the output via pipe also.

  I’m using a C# process to call ffmpeg like this :

  -f h264 -i pipe : -an -f mjpeg -q:v 1 pipe :

  I pipe in the source data stream using the process .StandardInput.BaseStream and get the returned data from .StandardOutput.BaseStream.

  The issue is, FFmpeg doesn’t send data. It sits, apparently waiting. No errors. Nothing gets written to StandardOutput.

  If I try each pipe on its own, it works fine. These work :

  a) passing in a source file location and getting the returned frame data via pipe (bytes are written to StandardOutput)

  b) passing in source bytes via pipe and asking Ffmpeg to save result to file

  This doesn’t work :

  c) piping in data, and getting data out via pipe.

  From a previous answer from @nmaier to this question (Can I use ffmpeg to output jpegs to a memory stream instead of a file) I think pipe-in/pipe-out should work. But it doesn’t.

  What am I doing wrong ?

  Thanks.

• Why is long video taking long time before VideoJS player gets metadata to start playing ?

  7 mars 2015, par Tom Jenkinson

  Does anyone know why it is taking so long before the loadedmetadata event is fired for longer videos ?

  Here is an example : https://www.la1tv.co.uk/player/124/260

  I can see in developer tools that the file is still downloading when the event is fired, so it’s not like it’s having to download the whole file, it’s just having to get quite far though before the event is fired.

  The ffmpeg command I am using to encode the video from java is :

  RuntimeHelper.executeProgram(new String[] {config.getString("ffmpeg.location"), "-y", "-nostdin", "-timelimit", ""+config.getInt("ffmpeg.videoEncodeTimeLimit"), "-progress", ""+f.progressFile.getAbsolutePath(), "-i", source.getAbsolutePath(), "-vf", "scale=trunc(("+f.h+"*a)/2)*2:"+f.h, "-strict", "experimental", "-acodec", "aac", "-b:a", f.aBitrate+"k", "-ac", "2", "-ar", "48000", "-vcodec", "libx264", "-vprofile", "main", "-g", "48", "-b:v", f.vBitrate+"k", "-maxrate", f.vBitrate+"k", "-bufsize", f.vBitrate*2+"k", "-preset", "medium", "-crf", "16", "-vsync", "vfr", "-af", "aresample=async=1000", "-movflags", "+faststart", "-r", f.fr+"", "-f", "mp4", f.outputFile.getAbsolutePath()}, workingDir, null, null);

  which can be found here.

  It has the faststart flag set and I thought this meant the metadata would be inserted right at the beginning of the file ?

  Could it be an issue with the encode settings ?

  Thanks !