Step 1 从视频中分离出音频（MP4->mp3）

def separateMp4ToMp3(tmp):
   mp4 = tmp.replace('.tmp', '.mp4')
   print('---> Separate the video clip {0}'.format(mp4))

   mp3 = tmp.replace('.tmp', '.mp3')
   if os.path.exists(mp3):
      print '\n\t{0} is detected. Skip. \n\tPlease delete .mp3 file if you need re-separate.'.format(mp3)
      return

   cmd = 'ffmpeg -i {0} -f mp3 -vn -loglevel fatal {1}'.format(mp4, mp3)
   print '\t{0}'.format(cmd)

   x = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

   for log in x.stdout.readlines():
      print '[ffmpeg info] {0}'.format(log)
   for log in x.stderr.readlines():
      print '[ffmpeg error] {0}'.format(log)

   print '\tSuccess! {0} -> {1}\n'.format(mp4, mp3)

Step 2 根据时间轴多个音频合成一份音频（MP3->mp3）

def composeMp3ToMp3(arr = []):
   if len(arr) <=0 :
      print('--->Operate audio array is empty!')
      return

   thisDir = os.path.dirname(arr[0])
   if (os.path.exists(thisDir + "/composeAudio.mp3")):
      print('--->{0}/composeAudio.mp3 is exist, if you need re-gennerate,Please delete it!'.format(thisDir))
      return

   print('---> Compose the audio :')
   var = ''
   for tem in arr:
      if os.path.exists(tem) == False:
         print '\n\t{0} is not exist! \n\tPlease make sure audio file be exist if you need compose.'.format(tem)
         return
      var = var + " -i " + tem

   if var == '':
      print '\n\t{0} is empty. \n\tPlease check .mp3 file if you need compose.'.format(var)
      return

   cmd = 'ffmpeg {0} -filter_complex amix=inputs=2:duration=first:dropout_transition=2 -f mp3 -loglevel fatal {1}/composeAudio.mp3'.format(var, thisDir)
   print '\t{0}'.format(cmd)
   x = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

   for log in x.stdout.readlines():
      print '[ffmpeg info] {0}'.format(log)
   for log in x.stderr.readlines():
      print '[ffmpeg error] {0}'.format(log)

   print '\tSuccess! {0} -> {1}\n'.format(var, thisDir + "/composeAudio.mp3")

Step 3 多个视频合成画中画效果<无声>（MP4->mp4）

def composeMp4ToMp4(arr = []):
   if len(arr) <= 0:
      print('--->Operate video array is empty!')
      return

   thisDir = os.path.dirname(arr[0])
   if (os.path.exists(thisDir + "/composeVideo.mp4")):
      print('--->{0}/composeVideo.mp4 is exist, if you need re-gennerate,Please delete it!'.format(thisDir))
      return

   print('---> Compose the video :')
   var = ''
   temparr = []
   for tem in arr:
      if os.path.exists(tem) == False:
         print '\n\t{0} is not exist! \n\tPlease make sure video file be exist if you need compose.'.format(tem)
         return

      #split image
      png = tem.replace('.mp4', '.png')
      tempcmd="ffmpeg -i {0} -ss 00:00:2.435 -loglevel fatal -vframes 1 {1}".format(tem, png)
      print '\t{0}'.format(tempcmd)
      x = subprocess.Popen(tempcmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
      x.wait()
      for log in x.stdout.readlines():
         print'[ffmpeg info] {0}'.format(log)
      for log in x.stderr.readlines():
         print'[ffmpeg error] {0}'.format(log)

      img = Image.open(png)
      imgSize = img.size
      #ipad
      if (imgSize[0] > imgSize[1]) :
         temparr.append(tem)
      #mobile
      else:
         var = var + " -i " + tem
      img.close()

   if (len(temparr) > 0):
      for tem in temparr:
         var = var + " -i " + tem

   if var == '':
      print '\n\t{0} is empty. \n\tPlease check video file if you need compose.'.format(var)
      return

   cmd = 'ffmpeg ' + var + ' -filter_complex "[1:v]scale=w=176:h=144:force_original_aspect_ratio=decrease[ckout];[0:v]' \
        '[ckout]overlay=x=W-w-10:y=10[out]" -map "[out]" -movflags faststart -loglevel fatal ' + thisDir + '/composeVideo.mp4'.format(var, thisDir)
   print '\t{0}'.format(cmd)
   x = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

   for log in x.stdout.readlines():
      print '[ffmpeg info] {0}'.format(log)
   for log in x.stderr.readlines():
      print '[ffmpeg error] {0}'.format(log)

   print '\tSuccess!\n {0} -> {1}\n'.format(var, thisDir + "/composeVideo.mp4")

Step 4 音频与视频合成

def communicateAudioVideo(folder):
   if (os.path.exists(folder + "/communicateVideo.mp4")):
      print('--->{0}/communicateVideo.mp4 is exist, if you need re-gennerate,Please delete it!'.format(folder))
      return

   if ((os.path.exists(folder + "/composeVideo.mp4") == False) or
         (os.path.exists(folder + "/composeAudio.mp3") == False)):
      print('--->{0}/composeVideo.mp4  or composeAudio.mp3 must be exist!'.format(folder))
      return

   print('---> Communicate the video :')
   cmd = 'ffmpeg -i ' + folder + '/composeVideo.mp4 -i ' + folder + '/composeAudio.mp3 -f mp4 ' \
         ' -loglevel fatal ' + folder +'/communicateVideo.mp4'
   print '\t{0}'.format(cmd)
   x = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

   for log in x.stdout.readlines():
      print '[ffmpeg info] {0}'.format(log)
   for log in x.stderr.readlines():
      print '[ffmpeg error] {0}'.format(log)

   print '\tSuccess!\n {0}  and {1} -> {2}\n'.format(folder + '/composeVideo.mp4', folder + '/composeAudio.mp3', folder +'/communicateVideo.mp4')

源码下载：https://github.com/wolf-song-ml/recording/tree/master

refer to:http://blog.csdn.net/wolfjson/article/details/76509709