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• Python/FFMPEG command line issues

  1er mars 2019, par 12hys

  I have a problem with running an FFMPEG command from within a Python script. When I run the following command from the terminal, I can stream video and audio from my attached webcam (Logitech C310) and output to file "out.avi" without any errors.

  ffmpeg -f alsa -i default -itsoffset 00:00:00 -f video4linux2 -s 1280x720 -r 25 -i /dev/video0 out.avi

  When I run the same command in a Python script below,

  def call_command(command):
  
      subprocess.Popen(command.split(' '))
  
  
  
  call_command("ffmpeg -f alsa -i default -itsoffset 00:00:00 -f video4linux2 -s 1280x720 -r 25 -i /dev/video0 out.avi")

  it gives me the error :

  Input #0, alsa, from 'default':
  
    Duration: N/A, start: 1317762562.695397, bitrate: N/A
  
    Stream #0.0: Audio: pcm_s16le, 44100 Hz, 1 channels, s16, 705 kb/s
  
  [video4linux2 @ 0x165eb10]Cannot find a proper format for codec_id 0, pix_fmt -1.
  
  /dev/video0: Input/output error

  Could anyone shed some light on what could be going on here ? I’ve tried using os.system() as well as subprocess.call() and it gives me the same errors. I’m not sure where to start on what could be going wrong here. I tried searching for the "video4linux2 Cannot find a proper format for codec_id 0, pix_fmt -1" error, but couldn’t find anything consistent.

  I’ve also tried putting the "ffmpeg -f..." command in a shell script "test.sh", and giving it executable permissions. I then open terminal, and run "./test.sh", and it works. When I try calling the command "./test.sh" from within my Python script, I’m left with the original error as before. This is the Python command I tried with the test.sh script :

  subprocess.call(["./test.sh"])

• HEVC video cutting issues using FFmpeg

  4 novembre 2017, par Dmitry Katkevich

  I need to cut videos using FFmpeg and I cannot transcode original videos (because of the performance reason). And I ran into a problem with HEVC videos from IPhone : there are glithes in the beginning of the cutted video.

  Here is how we converted videos before issue :

  ffmpeg.exe -i original.MOV -c:v copy -c:a aac -ss 4 -y good.mp4

  But for HEVC video there are glitches for 1 second in the beginning of the cutted video :

  

  Then I’ve tried to put seek option before input video :

  ffmpeg.exe -ss 4 -i original.MOV -c:v copy -c:a aac -y good.mp4

  The result seems good :

  

  After some googling it turns out that -ss option before input is faster but less accurate whereas -ss option after input and before output is slower but more accurate.

  So my questions are :

  • Why -ss option behaves differently then it is put before/after input ?

  • Is there a way to avoid glitches using output seek ffmpeg option ?

  • What does ’more/less accurate’ mean ? Does it mean that the seek may be too big or to little (bigger/less than we specified) ? How big may be this difference ?

• Issues with merging multiple audio files recorded by RecordRTC

  29 juillet 2019, par user590723

  I have been playing with RecordRTC a little bit. The audio input seem to be correctly sent to the web servers and saved on the drive.

  var recorder = RecordRTC(stream, {
  
  recorderType: MediaStreamRecorder,
  
  type: 'audio',
  
  mimeType: 'audio/wav',
  
  timeSlice: 2000,
  
  ondataavailable: function (blob) {                    
  
  
  
      var fileObject = new File([blob],  fileIndex + '-capture.wav', {
  
          type: 'audio/wav'
  
      });
  
  
  
      var formData = new FormData();
  
  
  
      formData.append('blob', fileObject);                    
  
      formData.append('filename', fileObject.name);
  
  
  
      $.ajax({
  
          url: 'XXX',
  
          data: formData,
  
          cache: false,
  
          contentType: false,
  
          processData: false,
  
          type: 'POST',
  
          success: function (response) {
  
              console.log('saved');
  
          }
  
      });
  
  
  
      fileIndex++;
  
  }

  }) ;

  I tried using ffmpeg to merge all the files into one, however every single time ffmpeg is crashing during parsing the second file :

  "Invalid data found when processing input"

  The command I am running is :

  ffmpeg.exe -f concat -safe 0 -i mylist.txt -c copy output.wav

  I would really appreciate if anyone could shed some light on what I am missing here.

  Thanks,
  M