Screenshot With JPEG XL Format Results in 16 Bit Depth Even the Original Video is 10 Bit Depth

[Jiang10086]

mpv Information

mpv v0.40.0-119-g1d1535ff9 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
 built on May 23 2025 00:13:48
libplacebo version: v7.351.0 (v7.351.0-dirty)
FFmpeg version: N-119684-g670089304
FFmpeg library versions:
   libavcodec      62.3.101
   libavdevice     62.0.100
   libavfilter     11.0.100
   libavformat     62.0.102
   libavutil       60.3.100
   libswresample   6.0.100
   libswscale      9.0.100

Other Information

- Windows version:Windows 11 24H2 (10.0.26100.1150)
- Source of mpv:[https://sourceforge.net/projects/mpv-player-windows/files/64bit-v3/](https://sourceforge.net/projects/mpv-player-windows/files/64bit-v3/)

Reproduction Steps

Set screenshot format to JPEG XL (screenshot-format=jxl in mpv.conf) and then screenshot a 10 bit video with the ‘s’ key

Expected Behavior

Screenshot image is 10 bit depth.

Actual Behavior

Screenshot image is 16 bit depth.

Log File

output.txt

Sample Files

[Nekomoe kissaten&LoliHouse] Zatsu Tabi - 08 [WebRip 1080p HEVC-10bit AAC ASSx2].mkv @00_00_04.jxl.zip

I carefully read all instruction and confirm that I did the following:

• [x] I tested with the latest mpv version to validate that the issue is not already fixed.
• [x] I provided all required information including system and mpv version.
• [x] I produced the log file with the exact same set of files, parameters, and conditions used in "Reproduction Steps", with the addition of --log-file=output.txt.
• [x] I produced the log file while the behaviors described in "Actual Behavior" were actively observed.
• [x] I attached the full, untruncated log file.
• [x] I attached the backtrace in the case of a crash.

[sfan5]

I guess #16161 should have fixed exactly this. @Traneptora any idea?

[hooke007]

But he didn't enable screenshot-sw ?

[Jiang10086]

I guess #16161 should have fixed exactly this. @Traneptora any idea?

I try to download the binary you mentioned and run .\mpv "video_path.mkv" --screenshot-format=jxl, then press "s", it shows can't take screenshot in JPEG XL format:

● Video  --vid=1                   (hevc 1920x1080 23.976 fps) [default]
● Audio  --aid=1  --alang=ja       'Stereo' (aac 2ch 44100 Hz) [default]
● Subs   --sid=1  --slang=zh-Hans  '简体中文' (ass) [default]
○ Subs   --sid=2  --slang=zh-Hant  '繁體中文' (ass)
AO: [wasapi] 48000Hz stereo 2ch float
VO: [gpu] 1920x1080 yuv420p10
Audio device underrun detected.
[screenshot] Could not open libavcodec encoder for saving images
[screenshot] Error writing file 'mpv-shot0001.jxl'!
Error writing screenshot!
[screenshot] Could not open libavcodec encoder for saving images
[screenshot] Error writing file 'mpv-shot0002.jxl'!
Error writing screenshot!
(Paused) AV: 00:06:28 / 00:23:40 (27%) A-V:  0.000 Dropped: 2
Exiting... (Quit)

[Jiang10086]

But he didn't enable screenshot-sw ?

I have try set "screenshot-sw=yes" in mpv.conf after your reply, but the screenshot remains 16 bits.

[sfan5]

I try to download the binary you mentioned and run [...]

Our CI builds do not come with libjxl. But there's no need to test this either way since you are on revision 1d1535ff9, which already includes this fix.

[Traneptora]

But he didn't enable screenshot-sw ?

I have try set "screenshot-sw=yes" in mpv.conf after your reply, but the screenshot remains 16 bits.

How are you determining that the screenshot is 16-bit?

[Traneptora]

I guess #16161 should have fixed exactly this. @Traneptora any idea?

My best guess is they're on libjxl 0.7 which doesn't include the bit depth header API. FFmpeg has it guarded by an #ifdef . They also need to be on at least ffmpeg/ffmpeg@fb823161a8e3dfc864a7bd83a9b968f4912c5b1d for that functionality to be in avcodec.

[hooke007]

https://github.com/shinchiro/mpv-winbuild-cmake/blob/master/packages/libjxl.cmake

Shin's build is always latest.

[Traneptora]

May be a regression, #16161 was supposed to fix exactly this. I'll investigate after work today. It isn't an issue with JPEG XL however as PNG also supports bit depth (via sBIT).

[Jiang10086]

But he didn't enable screenshot-sw ?

I have try set "screenshot-sw=yes" in mpv.conf after your reply, but the screenshot remains 16 bits.

How are you determining that the screenshot is 16-bit?

I have installed ImageMagick and run magick identify "Path\To\That\Image.jxl" and it shows JXL 1920x1080 1920x1080+0+0 16-bit sRGB 175106B 0.001u 0:00.001

[Traneptora]

I don't know if ImageMagick reads the bit depth header. You can try jxlinfo -v and it'll tell you, although I think it is actually 16-bit. I'll investigate when I get a bit more time.

[Jiang10086]

I don't know if ImageMagick reads the bit depth header. You can try jxlinfo -v and it'll tell you, although I think it is actually 16-bit. I'll investigate when I get a bit more time.

I have run it and it shows:

box: type: "JXL " size: 12, contents size: 4
JPEG XL file format container (ISO/IEC 18181-2)
box: type: "ftyp" size: 20, contents size: 12
box: type: "jxll" size: 9, contents size: 1
box: type: "jxlc" size: 175065, contents size: 175057
JPEG XL image, 1920x1080, lossy, 16-bit RGB+Alpha
num_color_channels: 3
num_extra_channels: 1
extra channel 0:
  type: Alpha
  bits_per_sample: 16
  alpha_premultiplied: 0 (Non-premultiplied)
have_preview: 0
have_animation: 0
Intrinsic dimensions: 1920x1080
Orientation: 1 (Normal)
Color space: RGB, D65, sRGB primaries, sRGB transfer function, rendering intent: Relative

And the alpha channel is unnecessary.

[Jiang10086]

I don't know if ImageMagick reads the bit depth header. You can try jxlinfo -v and it'll tell you, although I think it is actually 16-bit. I'll investigate when I get a bit more time.

Another issue is that I have set screenshot-jxl-distance=0.0, which according to the manual means lossless compression, but jxlinfo shows the screenshot is lossy. Seems like there are lots to do with MPV’s screenshot with JPEG XL format.

[L4cache]

Last time I checked, there's no actual 10bit support (gbrp10le) in FFmpeg libjxl ~(And there's no RGB30 in FFmpeg! It's libjxl wrapper currently only supports packed formats not planar, if this pattern is to be followed there must be a RGB30 format to begin with.)~ OK there's x2rgb10?? What's that? https://github.com/FFmpeg/FFmpeg/blob/167e343bbe75515a80db8ee72ffa0c607c944a00/libavcodec/libjxlenc.c#L690-L698

[Traneptora]

I don't know if ImageMagick reads the bit depth header. You can try jxlinfo -v and it'll tell you, although I think it is actually 16-bit. I'll investigate when I get a bit more time.

Another issue is that I have set screenshot-jxl-distance=0.0, which according to the manual means lossless compression, but jxlinfo shows the screenshot is lossy. Seems like there are lots to do with MPV’s screenshot with JPEG XL format.

I can reproduce the 16-bit issue, but not the lossy issue. When I try I use mpv --no-config --screenshot-format=jxl --screenshot-jxl-distance=0.0 --screenshot-sw=yes test.mkv. What did you try?

[Jiang10086]

I don't know if ImageMagick reads the bit depth header. You can try jxlinfo -v and it'll tell you, although I think it is actually 16-bit. I'll investigate when I get a bit more time.

Another issue is that I have set screenshot-jxl-distance=0.0, which according to the manual means lossless compression, but jxlinfo shows the screenshot is lossy. Seems like there are lots to do with MPV’s screenshot with JPEG XL format.

I can reproduce the 16-bit issue, but not the lossy issue. When I try I use mpv --no-config --screenshot-format=jxl --screenshot-jxl-distance=0.0 --screenshot-sw=yes test.mkv. What did you try?

I am sorry that I try screenshot again and it turns out a lossless compression, maybe the picture I used in jxlinfo is taken before I set screenshot-jxl-distance=0.0. Just forget about the lossy part.