[w][ffmpeg/video] h264: Late SEI is not implemented

Description

If reproducible, it would be nice if someone who is active on the appropriate FFmpeg channels could make them aware of the issue. Similar issues seem to have been addressed several times in the past, but evidently it might be a moving target.

System Information

System Version: macOS 26.5.1 (25F80)
Model Identifier: MacBookAir10,1
mpv-build   2025-11-02 9443097
mpv         2026-05-16 7d603534de
ffmpeg      2026-05-05 77c3a7349e

Reproduction Steps

$ mpv sample.mp4

Expected Behavior

No warnings

Actual Behavior

[ffmpeg/video] h264: Late SEI is not implemented. Update your FFmpeg version to the newest one from Git. If the problem still occurs, it means that your file has a feature which has not been implemented.

Log File

N/A

Sample Files

https://github.com/user-attachments/assets/c4fd791a-e8f8-4446-b67e-9e117cc76afc

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

• I tested and confirmed that the issue exists with the latest release version or newer.
• 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 by reproducing the warning with mpv sample.mp4 and the linked sample file, then inspect the FFmpeg H.264 handling implicated by the Late SEI message. Check whether the newest FFmpeg resolves it; if not, determine the appropriate FFmpeg channel for reporting the remaining behavior and confirm what outcome should replace the warning.