Output of yuv4mpegpipe doesn't have the same framerate as input video

mpv Information

mpv v0.41.0-dev-g41f6a6450 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
 built on Dec 21 2025 19:30:47
libplacebo version: v7.358.0
FFmpeg version: f853d12
FFmpeg library versions:
   libavcodec      62.11.100
   libavdevice     62.1.100
   libavfilter     11.4.100
   libavformat     62.3.100
   libavutil       60.8.100
   libswresample   6.1.100
   libswscale      9.1.100

Other Information

- Windows version: Windows 10 22H2
- GPU model, driver and version: NVIDIA GeForce RTX 5060 ver 32.0.15.9144
- Source of mpv: Latest stable release v0.41.0 41f6a64.
- Latest known working version: Unknown
- Issue started after the following happened: Unknown

Reproduction Steps

mpv --no-config input.mkv --audio=no --of=yuv4mpegpipe --ofopts=strict=experimental --gpu-debug --log-file=output.txt -o - > out.yuv

Expected Behavior

The yuv4mpegpipe copies the framerate from the input video

Actual Behavior

I haven't looked at how this works in the source code, but it appears the framerate and denominator don't get set at all, i can use videos with whatever framerate; in the YUV4 header the framerate will always be 24000:1 and there doesn't appear to be a way to overwrite it, which is problematic for when trying to pipe it to an encoder which tend to copy what's in the YUV4 header.
Before anyone questions it, i want to pass in the video through mpv since it renders .ass subtitles correctly and thus makes it the best way to hardsub a video, and i want a little more control over what encoder to use instead of relying what's in ffmpeg, the video i used for testing doesn't have any subtitles, but i just wanted to verify my observations.

Log File

log.txt

Sample Files

No response

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

• I tested with the latest mpv version to validate that the issue is not already fixed.
• I provided all required information including system and mpv version.
• 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.
• I produced the log file while the behaviors described in "Actual Behavior" were actively observed.
• I attached the full, untruncated log file.
• I attached the backtrace in the case of a crash.

Start with the yuv4mpegpipe output path exercised by the reported mpv command and inspect how the YUV4 header obtains its framerate and denominator. Reproduce with the exact command and a video using a non-24000:1 framerate; done means the generated header reflects the input framerate and remains usable by a downstream encoder.