#5637Subtitles delayed during playback speed change on macOS 26 Beta 6

IINA Version

1.4.0 beta 1 (Build 152), or 1.3.5

Release Channel

Beta

macOS Version

macOS 26 Beta 5 (25A5338b)

Steps to Reproduce

1. Run IINA on macOS 26 Beta 6.
2. Open any video file with embedded or external subtitles.
3. Set playback speed to 1.5× or higher.
4. Observe that subtitles appear delayed relative to audio/video.

Expected Behavior

Subtitles should remain in sync with the audio and video regardless of playback speed.

Actual Behavior

On macOS 26 Beta 6 (25A5338b), both 1.4.0-beta1 (Build 152) and 1.3.5 exhibit noticeable subtitle delay when playing videos at increased playback speeds (e.g., 2×). This issue did not occur on macOS 26 Beta 5 (25A5327h), playback and subtitle sync were normal there.

Workaround: Adding the following MPV option resolves the problem: video-sync=audio.

Update: Further testing turns out that video-sync=audio only helps briefly (i.e., only appears to work initially), the subtitle delay still gradually returns, so this option is not a reliable fix.

Crash Report or Process Sample

No response

Logs

No response

Update: See https://github.com/iina/iina/issues/5637#issuecomment-3181990153 and https://github.com/iina/iina/issues/5637#issuecomment-3182184671.

Sample Files

No response

How often can you reproduce the issue

Every time

Required Actions

• I tried my best to search from the existing issues (including closed issues) and didn't find duplicated issues.

Optional Actions

• I tested with the Nightly build and confirmed the issue is not fixed.
• I tested with the latest version of mpv and confirmed mpv doesn't have this issue.