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• FFmpeg : Combine video files with different start times

  18 mai 2016, par Fabian

  I have two webm files with audio and video recordings of a video conference session. Both files only contain one side of the conversation. They are not of the same length (someone has joined before the other one), but I have the unix timestamp in milliseconds of the start time of each video file.

  On a timeline they look like this :

  webm 1:   -----------------------------------------------
  
  webm 2:                 -----------------------------

  or like this :

  webm 1:   -----------------------------------------------
  
  webm 2:                          -----------------------------

  I would like to combine these two video files into one file so that :

  1. They appear next to each other (using the hstack option), and
  2. That they are mixed with taking the time stamps of the start times
     into account. The final video should then look like this :

  Target result : --------------===========================----

  The beginning and the end of the new video would show a black placeholder for the video file that has no data at this time of the mixed stream.

  At the moment I use this command :

  ffmpeg -i 1463408731413703.webm -i 1463408880317860.webm -filter_complex \
  
  "[0:v][1:v]hstack=inputs=2[v]; \
  
   [0:a][1:a]amerge[a]" \
  
  -map "[v]" -map "[a]" -ac 2  -c:v libvpx output.webm

  This creates a video like this :

  Not good result : =====================------------------

  i.e. the conversation is out of sync.

  How can I combine two video streams with different length and different start times using ffmpeg so that I will end up with "Target result" above ?

  Thanks a lot !

• Scheduled ffmpeg function gives thread.error and also fires ffmpeg too many times

  16 février 2016, par user2192778

  I want to record a clip of a radio stream every hour. Below is the code I am using to accomplish this so far.

      def sched(): # schedules a recording every hour
  
          def stream_record ():
  
              timeinfo = datetime.now().strftime('%Y%m%d_%H%M_%S%f')
  
              ffmpegEXE = "C:/path/to/ffmpeg.exe" 
  
              subprocess.call([ffmpegEXE, '-i', url, '-t', '00:07:00', 
  
              output_folder + timeinfo + '_' + str(start_minute) + 'url.mp3'], shell=True)
  
  
  
          i = 0
  
          while True:
  
  
  
          x = datetime.today()
  
          y=x.replace(day=x.day+1, hour=i, minute= start_minute, second=0, microsecond=0) 
  
          i = (i + 1) % 24
  
          delta_t=y-x
  
          secs=delta_t.seconds+1
  
          t = Timer(secs,stream_record)
  
          t.start()
  
  
  
  sched()

  Two things go wrong. (1) It will run, however an error reads :

  line X in (module)

  sched()

  line Y in sched

  t.start()

  line Z in start

  _start_new_thread(self.__bootstrap, ())

  thread.error : can’t start new thread

  And (2) when it runs, ffmpeg will initialize a recording anywhere from 5-15 times, saving many clips when I only want it to save one.

  How do I fix these errors and get ffmpeg to connect and record only one clip every hour ?

  I know this is an issue with the scheduling function ; the ffmpeg command works fine, as does the python script calling it.

• Setting HLS segment times

  16 février 2016, par James Townsend

  I am passing a processed video from openCV to ffmpeg via a pipe here is the code

  ./OpenCV & \
  
   tail -n +0 -f out.avi  | ffmpeg -i pipe:0  -hls_time 1 -hls_list_size 0 -hls_wrap 10 -hls_segment_filename '%03d.ts' stream.m3u8 

  My issue is the output .ts files are not in a uniformed duration they change from file to file.

  These are mostly long say 60 seconds. This means the connecting client has to wait for the first stream to finish before the playlist file (.m3u8) file is created. Therefor in this example they are 60 seconds or so behind live video and if the next .ts file is larger the streaming stops until this is finished. If the client tries to play before the next .ts file is created they are played the first .ts file.

  The frame rate from openCV is 1 frame per second.

  tail changes the output file of openCV called (out.avi) to a stdout.

  Any help would be great.