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• How to ensure plt.savefig saves multiple images instead of one ?

  18 mars 2018, par Natalie

  I’m trying to save images after for each iteration to show how my neural network is learning.

  for iterations in range(1,1000):
  
      model.fit(x_train, 
  
                y_train, 
  
                batch_size=20, 
  
                epochs=1, 
  
                verbose=2)
  
  
  
  predictions = model.predict(X)
  
  plt.plot(X,predictions,'o')
  
  plt.plot(r, morse(r,De,Re,alpha))
  
  plt.xlabel(r'$r$') # internuclear separation distance
  
  plt.ylabel(r'$V(r)$') # morse potential energy
  
  plt.savefig('myfig'+str(iterations))
  
  plt.clf()

  Originally, I was able to save every image, however, it now only saves the last iteration image only. I wondered how I might be able to solve this issue ?

  Also, related the first question : using the images I’m saving, I’m trying to merge all the images together into a quick movie to show the training process. I’ve been using ffmpeg (see image below for syntax error), but I keep getting syntax errors. Could anyone guide me through what I might be doing wrong ? ffmpeg syntax error I’m getting

  Thanks in advance for helping me out - completely new to machine learning but using it for a university project, so apologies for my lack of understanding/mistakes !!

• How can I retain 2x pixel density when encoding Retina screen capture with ffmpeg ?

  26 février 2018, par hfossli

  Whenever I use ffmpeg to encode a HiDPI/Retina screen recording, the video plays at 2x the size, so it looks fuzzy, because the pixel density is not retained.

  How can I retain the original pixel density of HiDPI screen recordings with ffmpeg ?

  How to reproduce :

  1. Use QuickTime Player to create a Screen Recording on a Retina Mac.
  2. Play the video you recorded in QuickTime Player using the ⌘1 Actual Size view. Notice that it’s playing 2:1 on your Retina Display, so the video looks sharp. It’s playing in half the space of the actual recorded pixels.

  3. Use ffmpeg to encode the video using a command like this :

     ffmpeg -i haha.mov -c:v libx264 -crf 23 haha-lg.mov

  4. Play the new ffmpeg-compressed video in QuickTime Player using the ⌘1 Actual Size view. Notice that it’s playing 1:1, so the video looks fuzzy.

  To clarify, the video does not look blurry because it was compressed. Rather, it looks blurry because the video is being played twice as big as it should be, at a 1:1 pixel density, instead of the required 2:1 pixel density, presumably because some metadata is being discarded when encoding.

  For the record, VLC plays both videos too big (blurry). So being able to play HiDPI videos seems to be a feature of QuickTime Player.

  Here is the detailed information ffmpeg shows for the original screen recording :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'haha.mov':
  
    Metadata:
  
      major_brand     : qt  
  
      minor_version   : 0
  
      compatible_brands: qt  
  
      creation_time   : 2018-02-26T16:46:00.000000Z
  
      com.apple.quicktime.make: Apple
  
      com.apple.quicktime.model: iMac18,3
  
      com.apple.quicktime.software: Mac OS X 10.13.3 (17D102)
  
      com.apple.quicktime.creationdate: 2018-02-26T10:45:50-0600
  
    Duration: 00:00:04.35, start: 0.000000, bitrate: 10947 kb/s
  
      Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1396x928 [SAR 1:1 DAR 349:232], 10701 kb/s, 60 fps, 60 tbr, 6k tbn, 12k tbc (default)
  
      Metadata:
  
        creation_time   : 2018-02-26T16:46:00.000000Z
  
        handler_name    : Core Media Data Handler
  
        encoder         : H.264

  And here is the information for the ffmpeg-compressed version :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'haha-lg.mov':
  
    Metadata:
  
      major_brand     : qt  
  
      minor_version   : 512
  
      compatible_brands: qt  
  
      encoder         : Lavf57.83.100
  
    Duration: 00:00:04.35, start: 0.000000, bitrate: 1923 kb/s
  
      Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1396x928 [SAR 1:1 DAR 349:232], 1783 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
  
      Metadata:
  
        handler_name    : DataHandler
  
        encoder         : Lavc57.107.100 libx264

• How can I retain 2x pixel density when encoding Retina screen capture with ffmpeg ?

  26 février 2018, par hfossli

  Whenever I use ffmpeg to encode a HiDPI/Retina screen recording, the video plays at 2x the size, so it looks fuzzy, because the pixel density is not retained.

  How can I retain the original pixel density of HiDPI screen recordings with ffmpeg ?

  How to reproduce :

  1. Use QuickTime Player to create a Screen Recording on a Retina Mac.
  2. Play the video you recorded in QuickTime Player using the ⌘1 Actual Size view. Notice that it’s playing 2:1 on your Retina Display, so the video looks sharp. It’s playing in half the space of the actual recorded pixels.

  3. Use ffmpeg to encode the video using a command like this :

     ffmpeg -i haha.mov -c:v libx264 -crf 23 haha-lg.mov

  4. Play the new ffmpeg-compressed video in QuickTime Player using the ⌘1 Actual Size view. Notice that it’s playing 1:1, so the video looks fuzzy.

  To clarify, the video does not look blurry because it was compressed. Rather, it looks blurry because the video is being played twice as big as it should be, at a 1:1 pixel density, instead of the required 2:1 pixel density, presumably because some metadata is being discarded when encoding.

  For the record, VLC plays both videos too big (blurry). So being able to play HiDPI videos seems to be a feature of QuickTime Player.

  Here is the detailed information ffmpeg shows for the original screen recording :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'haha.mov':
  
    Metadata:
  
      major_brand     : qt  
  
      minor_version   : 0
  
      compatible_brands: qt  
  
      creation_time   : 2018-02-26T16:46:00.000000Z
  
      com.apple.quicktime.make: Apple
  
      com.apple.quicktime.model: iMac18,3
  
      com.apple.quicktime.software: Mac OS X 10.13.3 (17D102)
  
      com.apple.quicktime.creationdate: 2018-02-26T10:45:50-0600
  
    Duration: 00:00:04.35, start: 0.000000, bitrate: 10947 kb/s
  
      Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1396x928 [SAR 1:1 DAR 349:232], 10701 kb/s, 60 fps, 60 tbr, 6k tbn, 12k tbc (default)
  
      Metadata:
  
        creation_time   : 2018-02-26T16:46:00.000000Z
  
        handler_name    : Core Media Data Handler
  
        encoder         : H.264

  And here is the information for the ffmpeg-compressed version :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'haha-lg.mov':
  
    Metadata:
  
      major_brand     : qt  
  
      minor_version   : 512
  
      compatible_brands: qt  
  
      encoder         : Lavf57.83.100
  
    Duration: 00:00:04.35, start: 0.000000, bitrate: 1923 kb/s
  
      Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1396x928 [SAR 1:1 DAR 349:232], 1783 kb/s, 60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
  
      Metadata:
  
        handler_name    : DataHandler
  
        encoder         : Lavc57.107.100 libx264