--untimed performance regression since commit e3af545

[owl0w1]

Important information

Version information:

• mpv version: current master
• Linux Distribution and Version: Ubuntu 24.04
• Source of the mpv binary: compiled from source
• Version of mpv that introduced the problem: commit e3af545

Reproduction steps

While setting up fuzzing of mpv, I noticed that execution with benchmark options (--untimed and friends) is significantly slower in current master than release 0.37.0. git bisect located the problem at commit e3af545.

First bad commit:

1. Check out commit e3af545
2. Build from source
3. Benchmark performance of --untimed option

user@laptop:~/mpv-e3af545$ hyperfine './build/mpv --vo=null --untimed --ao=null --ao-null-untimed ~/9bitwhite.mkv'
Benchmark 1: ./build/mpv --vo=null --untimed --ao=null --ao-null-untimed ~/9bitwhite.mkv
  Time (mean ± σ):     515.6 ms ±   5.0 ms    [User: 216.0 ms, System: 51.4 ms]
  Range (min … max):   509.9 ms … 527.5 ms    10 runs
 
user@laptop:~/mpv-e3af545$ hyperfine './build/mpv --untimed ~/9bitwhite.mkv'
Benchmark 1: ./build/mpv --untimed ~/9bitwhite.mkv
  Time (mean ± σ):      1.951 s ±  0.018 s    [User: 0.342 s, System: 0.107 s]
  Range (min … max):    1.932 s …  1.982 s    10 runs

A 9 second video file took roughly 0.5s to play with vo=null and --untimed options. With normal video output and --untimed option only, it took roughly 1.9s to play.

Last good commit:

1. Check out commit 7051e94, parent of commit e3af545
2. Build from source
3. Benchmark performance of --untimed option

user@laptop:~/mpv-7051e94$ hyperfine './build/mpv --vo=null --untimed --ao=null --ao-null-untimed ~/9bitwhite.mkv'
Benchmark 1: ./build/mpv --vo=null --untimed --ao=null --ao-null-untimed ~/9bitwhite.mkv
  Time (mean ± σ):     101.7 ms ±   3.1 ms    [User: 206.8 ms, System: 53.0 ms]
  Range (min … max):    95.7 ms … 108.8 ms    27 runs
 
user@laptop:~/mpv-7051e94$ hyperfine './build/mpv --untimed ~/9bitwhite.mkv'
Benchmark 1: ./build/mpv --untimed ~/9bitwhite.mkv
  Time (mean ± σ):      1.618 s ±  0.019 s    [User: 0.375 s, System: 0.093 s]
  Range (min … max):    1.593 s …  1.650 s    10 runs

The same 9 second video file took roughly 0.1s to play with vo=null and --untimed options. With normal video output and --untimed option only, it took roughly 1.6s to play.

There is a 5x performance regression in --untimed between these two commits.

Expected behavior

Do not sleep when outputting video frames with --untimed enabled.

Actual behavior

Additional delay other than decoding cost introduced between frames even when --untimed is enabled.

Sample files

The sample file used in reproduction steps: https://github.com/strongcourage/fuzzing-corpus/blob/master/mkv/9bitwhite.mkv

The issue seems to be independent of the input file.

[llyyr]

can you try #13614 ?

[owl0w1]

#13614 fixes the issue.

Benchmark:

user@laptop:~/mpv-410a9cd$ hyperfine './build/mpv --vo=null --untimed --ao=null --ao-null-untimed ~/9bitwhite.mkv'
Benchmark 1: ./build/mpv --vo=null --untimed --ao=null --ao-null-untimed ~/9bitwhite.mkv
  Time (mean ± σ):     120.7 ms ±   6.6 ms    [User: 267.8 ms, System: 56.3 ms]
  Range (min … max):   113.1 ms … 138.4 ms    26 runs