[FFmpeg-trac] #7045(undetermined:new): Should retain pixel density metadata from HiDPI/Retina screen recordings
FFmpeg
trac at avcodec.org
Mon Feb 26 19:49:05 EET 2018
#7045: Should retain pixel density metadata from HiDPI/Retina screen recordings
-------------------------------------+-------------------------------------
Reporter: moubry | Type: defect
Status: new | Priority: normal
Component: | Version:
undetermined | unspecified
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Summary of the bug:
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. I expect videos encoded with ffmpeg to retain whatever metadata
is used by players (like QuickTime Player) to play HiDPI/Retina videos at
the expected size.
I'm experiencing this issue on a Mac, but it might be an issue across
other platforms with HiDPi displays as well.
{{{
$ ffmpeg version
ffmpeg version 3.4.2 Copyright (c) 2000-2018 the FFmpeg developers
built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
}}}
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.
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
}}}
--
Ticket URL: <https://trac.ffmpeg.org/ticket/7045>
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