Bug: Playback seeks backwards when speed is increased, and seeks forwards when speed is decreased

[mesvam]

Important Information

Provide following Information:

• mpv version:

> mpv --version
mpv v0.37.0-337-gbd5b80ba Copyright © 2000-2024 mpv/MPlayer/mplayer2 projects
 built on Feb 18 2024 00:09:08
libplacebo version: v6.338.0-77-g3ba18d5-dirty
FFmpeg version: N-113670-g0895ef0d6
FFmpeg library versions:
   libavutil       58.39.100
   libavcodec      60.39.101
   libavformat     60.21.100
   libswscale      7.6.100
   libavfilter     9.17.100
   libswresample   4.13.100

• Platform and Version: Windows 11
• Source of the mpv binary: https://sourceforge.net/projects/mpv-player-windows/files/64bit-v3/mpv-x86_64-v3-20240218-git-bd5b80b.7z/download
• If known which version of mpv introduced the problem: unknown
• GPU model, driver and version: GTX 1080
• Possible screenshot or video of visual glitches: none

Reproduction steps

• Start with clean config/profile
• add this debug script to the profile under the scripts directory

require 'mp.msg'
mp.set_property("msg-level", string.format("%s=debug", mp.get_script_name()))

local function s1()
    local before = mp.get_property_native('audio-pts')
    mp.msg.debug(string.format("before: %f", before))
    mp.set_property_native("speed", 1)
    local after = mp.get_property_native('audio-pts')
    mp.msg.debug(string.format("after : %f", after))
    mp.msg.debug(string.format("diff  : %f", after-before))
end
local function s2()
    local before = mp.get_property_native('audio-pts')
    mp.msg.debug(string.format("before: %f", before))
    mp.set_property_native("speed", 4)
    local after = mp.get_property_native('audio-pts')
    mp.msg.debug(string.format("after : %f", after))
    mp.msg.debug(string.format("diff  : %f", after-before))
end

mp.add_key_binding("1", "slow", s1)
mp.add_key_binding("2", "fast", s2)

• play a video or audio file from the console (e.g. mpv.com video.mkv) to show debug messages
• toggle the speed with the keys 1 and 2 during playback. 1 sets speed to 1x and 2 sets speed to 4x
• If necessary, use screen capture software or a phone to record the screen to capture video seeking behavior

Expected behavior

Playback time should not change (no seeking). audio-pts before and after the speed change should be identical or very close. Ideally the console should show something like

[debug] before: 12.071627
[debug] after : 12.071627
[debug] diff  : 0

Actual behavior

The player actually seems to seek backwards and forwards by a set duration when the speed changes, as seen on the OSD. There is a large difference in audio-pts before and after the speed change.

[debug] before: 12.071627
[debug] after : 11.263086
[debug] diff  : -0.808541

The time difference increases as the speed difference increases. In severe cases, when the speed changes a lot (e.g. from 1x to 16x), audio-pts can actually be negative, seeking beyond the boundaries of the file. Here is the output for a 1x to 16x speed change.

[debug] before: 1.047906
[debug] after : -3.047085
[debug] diff  : -4.094991

mpv seeks the file to -3.047085 and the difference is over 4 seconds!

Why this matters: I have scripts that depend on always having accurate playback time

Log file

mpv.log

Sample files

Any video or audio file will work, but if you use this diagnostic video https://www.youtube.com/watch?v=szoOsG9137U (download with yt-dlp), you can clearly see the video seeking on a screen recording