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• How to capture a timed screen recording on a Mac with ffmpeg

  28 septembre 2016, par wetjosh

  I’m on a Mac with MacOS Sierra installed. I’ve installed ffmpeg with homebrew. I list my devices via :

  ffmpeg -f avfoundation -list_devices true -i ""

  which returns :

  [AVFoundation input device @ 0x7fc2de40e840] AVFoundation video devices:
  
  [AVFoundation input device @ 0x7fc2de40e840] [0] FaceTime HD Camera
  
  [AVFoundation input device @ 0x7fc2de40e840] [1] Capture screen 0
  
  [AVFoundation input device @ 0x7fc2de40e840] AVFoundation audio devices:
  
  [AVFoundation input device @ 0x7fc2de40e840] [0] Built-in Microphone

  I don’t need audio so I start my 5 second screen recording via :

  ffmpeg -f avfoundation -t '5' -i '1' test.mov

  It creates an mov file in the working directory but doesn’t stop after 5 seconds. In fact, I can’t even stop the recording as it suggests by pressing ’q’. Ctl-C doesn’t work either, and I am left with force quitting via Activity Monitor. I’ve tried this same command but using device 0 (FaceTime camera) and it stops after 5 seconds.

  If someone can solve that riddle, my next question is how can I watch the newly created file in quicktime (I’m thinking I’ll need to encode or decode or something) because even the FaceTime video file would not open in QuickTime. It just says "The document could not be opened". It does, however, open with VLC.

  UPDATE : I’ve tried this on an older OS (Yosemite) and got the same results (thought it might be the new OS that broke it).

• ffmpeg livestream only shows one frame at a time

  28 octobre 2016, par user3308335

  So, I’ve tried to turn one of my pis into a silly "baby cam" for my pet and I followed the tutorial made by Ustream.tv on how to do this.

  This is the script I run to start the stream :

  #!/bin/bash
  
  RTMP_URL=<rtmpurl>
  
  STREAM_KEY=<streamkey>
  
  while :
  
  do
  
    raspivid -n -hf -t 0 -w 640 -h 480 -fps 15 -b 400000 -o - | ffmpeg -i - -vcodec copy -an  -f flv $RTMP_URL/$STREAM_KEY
  
    sleep 2
  
  done
  
  </streamkey></rtmpurl>

  However, whenever I go to view the stream, the stream shows only one frame. The same frame until I refresh the browser, watch the ad again, and then it’s a new same frame that it’ll show.

  Does anyone have an idea why this might be happening or any troubleshooting tricks for me to try ?

• Unusual results extracting VP9 pkt_size with ffprobe as compared to H.264

  26 novembre 2016, par Jeff S.

  I’m trying to graph the bitrate over time for H.264 and VP9 videos by extracting the frame size with ffprobe, but many of the VP9 videos are showing significantly lower bitrate and total size than both the file size would indicate and that ffprobe reports.

  Can someone point me in the right direction for finding the missing bytes ?

  For example :

  # The extracted values and the ffprobe values are very close for mp4
  
  Video Codec: h264
  
  Video Bitrate: 0.668869
  
  Frame Bitrate: 0.665552571931
  
  Video Size: 6381536.0
  
  Frame Total Size: 6349891
  
  
  
  # The extracted values and the ffprobe values are very different for some vp9 videos
  
  Video Codec: vp9
  
  Video Bitrate: 0.600966
  
  Frame Bitrate: 0.375144984531
  
  Video Size: 5730519.0
  
  Frame Total Size: 3577195

  Below is what I’m using for validation. Note that the sample videos do not contain audio.

  import subprocess
  
  import json
  
  
  
  def export_video_info(video_id):
  
      proc = subprocess.Popen(['ffprobe',
  
          '-v', 'quiet', '-print_format', 
  
          'json', '-show_format',
  
          '-show_streams', '-show_frames',
  
          video_id
  
          ],
  
          stdout=subprocess.PIPE,
  
      )
  
      return proc.communicate()[0]
  
  
  
  # Example video:  https://www.youtube.com/watch?v=g_OdgCrnzYo
  
  # youtube-dl --id -f 135 https://www.youtube.com/watch?v=g_OdgCrnzYo
  
  # youtube-dl --id -f 244 https://www.youtube.com/watch?v=g_OdgCrnzYo
  
  video_list = ['g_OdgCrnzYo.mp4', 'g_OdgCrnzYo.webm']
  
  
  
  '''
  
  Format for every frame: 
  
  
  
      {
  
          "media_type": "video",
  
          "key_frame": 0,
  
          "pkt_pts": 84484,
  
          "pkt_pts_time": "84.484000",
  
          "pkt_dts": 84484,
  
          "pkt_dts_time": "84.484000",
  
          "best_effort_timestamp": 84484,
  
          "best_effort_timestamp_time": "84.484000",
  
          "pkt_duration": 33,
  
          "pkt_duration_time": "0.033000",
  
          "pkt_pos": "7103361",
  
          "pkt_size": "28",
  
          "width": 854,
  
          "height": 480,
  
          "pix_fmt": "yuv420p",
  
          "sample_aspect_ratio": "1:1",
  
          "pict_type": "P",
  
          "coded_picture_number": 0,
  
          "display_picture_number": 0,
  
          "interlaced_frame": 0,
  
          "top_field_first": 0,
  
          "repeat_pict": 0
  
      },
  
  '''
  
  
  
  
  
  # NOTE: videos do not include audio
  
  for video in video_list:
  
      output = json.loads(export_video_info(video))
  
      ff_bitrate = float(output['format']['bit_rate']) / 10**6
  
      ff_duration = float(output['format']['duration'])
  
      ff_codec = output['streams'][0]['codec_name']
  
      ff_size = float(output['format']['size'])
  
      frame_size_sum = 0
  
      for val, items in enumerate(output['frames']):
  
          if output['frames'][val]['media_type'] == 'video': 
  
              frame_size_sum += int(output['frames'][val]['pkt_size'])
  
  
  
      frame_bitrate = frame_size_sum / ff_duration * 8 / 10**6
  
      print('Video Codec: {}\nVideo Bitrate: {}\nFrame Bitrate: {}\nVideo Size: {}\nFrame Total Size: {}\n\n'.format(ff_codec, ff_bitrate, frame_bitrate, ff_size, frame_size_sum))