`--audio-spdif=<codec>` passthrough not working with spdif

mpv Information

mpv v0.39.0-502-ge52f9758 Copyright © 2000-2024 mpv/MPlayer/mplayer2 projects
 built on Dec 14 2024 00:11:14
libplacebo version: v7.350.0 (v7.349.0-30-g056b852-dirty)
FFmpeg version: N-118070-g17e474668
FFmpeg library versions:
   libavcodec      61.27.101
   libavdevice     61.4.100
   libavfilter     10.6.101
   libavformat     61.9.101
   libavutil       59.51.100
   libswresample   5.4.100
   libswscale      8.12.100

Other Information

- Windows version:
Microsoft Windows [Version 10.0.19045.5247]
- GPU model, driver and version:
	Intel(R) HD Graphics 5500

	Driver version:	20.19.15.4531
	Driver date:	29/09/2016
	DirectX version:	12 (FL 11.1)
- Source of mpv:
https://github.com/shinchiro/mpv-winbuild-cmake/releases
- Latest known working version:
/
- Issue started after the following happened:
/

Reproduction Steps

mpv --no-config --audio-spdif=truehd Triangle.of.Sadness.2022.BluRay.TrueHD.7.1.Atmos.outro.mka

Expected Behavior

atmos data gets passed through correctly

Actual Behavior

popping sound on the speakers, spdif doesn't get passed through correctly
using a Marantz ki pearl & a marantz network audio player na7004

Log File

output.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 exact reproduction command and compare its behavior with output.txt, using the listed mpv, Windows, and receiver details as context. Trace the SPDIF/TrueHD passthrough path from the command-line option, then validate the result with the supplied MKA file or equivalent hardware setup. Done means Atmos data passes through without popping.