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Videos trimmed by Quicktime fail to play properly
Important Information
Provide following Information:
- mpv version: 0.34.1
- macOS Version: 12.4
- Source of the mpv binary or bundle: stolendata
- If known which version of mpv introduced the problem: unknown
- Possible screenshot or video of visual glitches
The visual glitch is that shortly after playback starts the video freezes for a while before continuing to play. One aspect of the problem can be seen in this screenshot taken before playback has started by using the --pause option. Notice the current playback position timestamp in the on screen controller is negative:
Shouldn't this option, which is enabled by default, have insured the start time is 0?:
--rebase-start-time=<yes|no> Whether to move the file start time to 00:00:00 (default: yes). This is less awkward for files which start at a random timestamp, such as transport streams. On the other hand, if there are timestamp resets, the resulting behavior can be rather weird. For this reason, and in case you are actually interested in the real timestamps, this behavior can be disabled with no.
Reproduction steps
Merely play the linked video in the sample files section below. The video will start playing without audio. Then the video will freeze. At that point the audio will start playing. Eventually video playback will resume.
The origin of this issue is IINA issue https://github.com/iina/iina/issues/3848. The reporter of that issue has been using Quicktime on a Mac to trim videos. The resulting videos play fine using Quicktime or VLC, but exhibit the undesirable behavior when starting playback if played under IINA or mpv.
The playback behavior experienced in this issue matches the behavior reported in issue https://github.com/mpv-player/mpv/issues/8876. However that issue concerns videos cut by FFmpeg running under Linux and as pointed out in that issue there are other ways to cut files using FFmpeg, for example using the avoid_negative_ts option. This issue with videos trimmed by Quicktime is more of a problem as Quicktime does not provide Mac users any options on how videos are trimmed.
As in https://github.com/mpv-player/mpv/issues/8876 mpv is reporting A/V desynchronization when playing the file created by Quicktime:
[ 21.895][w][cplayer] Audio/Video desynchronisation detected! Possible reasons include too slow
To create a video that demonstrates this problem:
- Pick a video that has large gaps between I-frames
- Open the video on a Mac with using Quicktime
- Use the Quicktime trim feature to trim away some of the start of the video
- Save the trimmed video
- Play the trimmed video using mpv looking for glitches when playback begins
How severe the playback glitch is depends upon where the video is cut in relation to I-frames.
Expected behavior
Mac users trimming a file using Quicktime expect the resulting file will play without glitches using IINA, mpv, Quicktime or VLC.
Actual behavior
The video starts playing without audio. Then the video freezes and the audio starts playing. Eventually the video resumes playing.
Log file
https://0x0.st/oQj7.log
The log file was generated by running mpv like so:
low-batt@gag quicktime-issue$ /Applications/mpv.app/Contents/MacOS/mpv -no-config -v -v --log-file=low-batt-mpv-quicktime-trim-issue.log --pause --script-opts=osc-visibility=always low-batt-mpv-quicktime-trim-issue.mp4
Sample files
https://0x0.st/oQjF.mp4
This is the video low-batt-mpv-quicktime-trim-issue.mp4 created by using the Quicktime trim function.
on my end with --video-sync=display-resample at least the glitch is gone. audio still starts late or rather the video starts too early compared to vlc or quicktime.
what i observed vlc and quicktime start the video at a later point of time, mpv on the other hand shows ~3sec more video at the beginning (the reason why the audio is probably missing). which suggests the video is wrongly 'trimmed'/'offset' within mpv internally, eg it might need to ignore those early video frames(?).
vlc isn't completely glitch free here either. it sometimes shows the first frame (the same as on mpv) and sometimes doesn't and is also 'stuck' for a little bit in some cases at the beginning.
to demonstrate what i mean.
i am not sure if this is a decode, demuxer oder metadata problem. this problem should not be mac specific, maybe someone can confirm? i would remove the mac label in that case.
Anyone know if the MPEG standard has anything to say about how a compliant player should behave given this file?
FFprobe shows the file has several seconds of video before audio starts.
FFprobe Output:
low-batt@gag quicktime-issue$ ffprobe -of compact -show_packets -show_entries packet=codec_type,pts_time low-batt-mpv-quicktime-trim-issue.mp4
ffprobe version 5.0.1 Copyright (c) 2007-2022 the FFmpeg developers
built with Apple clang version 13.1.6 (clang-1316.0.21.2)
configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/5.0.1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-neon
libavutil 57. 17.100 / 57. 17.100
libavcodec 59. 18.100 / 59. 18.100
libavformat 59. 16.100 / 59. 16.100
libavdevice 59. 4.100 / 59. 4.100
libavfilter 8. 24.100 / 8. 24.100
libswscale 6. 4.100 / 6. 4.100
libswresample 4. 3.100 / 4. 3.100
libpostproc 56. 3.100 / 56. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'low-batt-mpv-quicktime-trim-issue.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf59.16.100
Duration: 00:00:15.05, start: 0.000000, bitrate: 2727 kb/s
Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1280x720 [SAR 1:1 DAR 16:9], 1953 kb/s, 60 fps, 60 tbr, 15360 tbn (default)
Metadata:
handler_name : Core Media Video
vendor_id : [0][0][0][0]
Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 341 kb/s (default)
Metadata:
handler_name : Core Media Audio
vendor_id : [0][0][0][0]
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Playing with VLC some more I was able to see a small glitch at startup. Pausing VLC and backing it up shows it does initially show the same frame as mpv, but then quickly skips to the point where audio starts.
Shouldn't this option, which is enabled by default, have insured the start time is 0?:
That is not true for mp4 files, just checked for 10 second positive video from Apple TV+, mpv prints 09 seconds for audio, for video and same 10 seconds (you cannot force 9 seconds) for audio (audio is still at 9 seconds)+video. Instead of doing gapless audio for AAC and EAC3 as everyone else (using an editlist for track 2 (audio track)), they just put audio timestamps before video, while video timestamps start at 10 perfectly.
Same happens here.
There is also an editlist with strange value in media time for track 1 (video). In fact VLC corrupts the video.
