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

Question

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

Answer 1

FFmpeg currently doesn't support that type of metadata. If you can provide a (short) sample on FFmpeg's bug tracker, we can probably add support for this type of metadata to future versions.