frame-back-step not working for audio files

mpv Information

mpv v0.40.0 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
 built on May  7 2025 22:20:34
libplacebo version: v7.349.0
FFmpeg version: 6.1.2
FFmpeg library versions:
   libavcodec      60.31.102
   libavdevice     60.3.100
   libavfilter     9.12.100
   libavformat     60.16.100
   libavutil       58.29.100
   libswresample   4.12.100
   libswscale      7.5.100

Other Information

- macOS version: 15.6
- Source of mpv: github
- Latest known working version: N/A
- Issue started after the following happened: N/A

Reproduction Steps

Reproducible with --no-config.

1. open audio file
2. skip to somewhere in the middle
3. click on the UI (HUD?) to display milliseconds
4. try using frame-step (.) and frame-back-step (,)

Expected Behavior

As we cant speak of "frames" in an audio file, I will just refer to the milliseconds positions. On pressing either key, the ms should skip forward or backwards. On holding either key, mpv should either play in (nearly) normal speed or play backwards in nearly 100% backwards speed.

Actual Behavior

• Pressing frame-step once does not advance the ms position. Even hitting the key repeatedly does not advance the position. I havent figured out the exact behavior but on rare occasions it does indeed skip forward. Like every 20 key presses or so.
• Holding down frame-step works as intended. The audio is played as if played normally.
• Pressing frame-back-step once does absolutely nothing.
• Holding down frame-back-step does very little. For every 4-5 seconds holding down the key, the player position will step back 1 millisecond. Defacto not useable at all.

Additional findings:

• frame-back-step works fine on video, though I noticed it does not play audio while stepping backwards. I remember this worked fine in a previous version.
• Also, these issues with audio files could explain some of the other open issues mentioning frame-back-step (e.g. #11471)

Log File

N/A

P.S.: I would not have checked all the checkboxes of the "read all instructions" area, but they are required.

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.

Reproduce the issue with mpv v0.40.0 and --no-config using an audio file, then trace the frame-step and frame-back-step command paths and their audio playback behavior. Done means repeated single steps move the millisecond position reliably, backward stepping works at a usable rate, and holding either key provides the expected playback behavior without regressing video stepping.