[ffmpeg] mp4: track 1: codec frame size is not set

[Rochkiller]

mpv Information

mpv v0.41.0-690-g1ac687d79 Copyright © 2000-2026 mpv/MPlayer/mplayer2 projects
 built on May 26 2026 13:45:37
libplacebo version: v7.364.0 (v7.360.0-57-g051cc36-dirty)
FFmpeg version: N-124653-g0ac3b00a1
FFmpeg library versions:
   libavcodec      62.34.102
   libavdevice     62.4.100
   libavfilter     11.17.100
   libavformat     62.18.100
   libavutil       60.31.100
   libswresample   6.4.100
   libswscale      9.7.100

Other Information

- Windows version: Windows 10 IoT Entreprise LTSC 21H2
- GPU model, driver and version: AMD Radeon RX 9070 XT - 32.0.31007.5012 - 26.5.2
- Source of mpv: zhongfly/mpv-winbuild
- Latest known working version: Idk, issue still occurs with oldest build available : mpv-x86_64-v3-20260428-git-a42b1b9103
- Issue started after the following happened: N/A

Reproduction Steps

1. Open an Youtube video with lastest zhongfly/mpv-winbuild
2. Dump-cache

Also, same happen with Kick live stream but with this error (red) :

[ffmpeg] mp4: sample rate not set
[recorder] Writing header failed.
Cache dumping stopped due to error.

I don't know if it's the same issue but the result is the same (1MiB outfile not playable)

FYI, same happen with build shinchiro/mpv-winbuild-cmake since build mpv-x86_64-v3-20260517-git-059bc70 : shinchiro/mpv-winbuild-cmake#828

Expected Behavior

Example from shinchiro/mpv-winbuild-cmake mpv-x86_64-v3-20260416-git-d20d108 :
mpv https://youtu.be/hrk8ZhjoB-Q

[auto_profiles] Applying auto profile: youtube
[osd/libass] fontselect: Using default font family: (mpv-osd-symbols, 400, 0) -> ArialMT, 0, ArialMT
Not seekable, but enabling seeking on user request.
● Video --vid=1 (h264 1920x1080 59.9401 fps 3298 kbps) [default]
● Audio --aid=1 --alang=eng (aac 2ch 44100 Hz 128 kbps) [default]
File tags:
Date: 20191121
Uploader: Danucd
Channel_URL: https://www.youtube.com/channel/UCsIiIEGRoBILi8LSkWNPqXA
AO: [wasapi] 192000Hz stereo 2ch float
VO: [gpu-next] 1920x1080 yuv420p
[modernz] URL detected.
[modernz] Approximating file size...
[modernz] Executing: yt-dlp -f (bv*[vcodec~='^(av(0|c)1)']+ba[acodec^=mp4a])/b --no-download -O %(filesize,filesize_approx)s https://youtu.be/hrk8ZhjoB-Q
[osd/libass] fontselect: Using default font family: (mpv-osd-symbols, 400, 0) -> ArialMT, 0, ArialMT
[modernz] Download size: 31.91 MiB
Cache dumping started.
[ffmpeg] mp4: track 0: codec frame size is not set
[recorder] This is an experimental feature. Output files might be broken or not play correctly with various players (including mpv itself).
[recorder] Discontinuity at timestamp 0.000000.
Cache dumping successfully ended.
AV: 00:00:11 / 00:01:16 (16%) A-V: 0.000 Cache: 64s/30MB
Exiting... (Quit)

Outfile 32MiB playable
warning [ffmpeg] mp4: track 0: codec frame size is not set

Actual Behavior

mpv https://youtu.be/hrk8ZhjoB-Q

[auto_profiles] Applying auto profile: youtube
[osd/libass] fontselect: Using default font family: (mpv-osd-symbols, 400, 0) -> ArialMT, 0, ArialMT
Not seekable, but enabling seeking on user request.
● --edition=0 '299 - 1920x1080 (1080p60) (h264 60 fps 3353 kbps)'
○ --edition=1 '301 - 1920x1080 muxed-14 (h264 60 fps) (aac)'
○ --edition=2 '298 - 1280x720 (720p60) (h264 60 fps 1605 kbps)'
○ --edition=3 '300 - 1280x720 muxed-12 (h264 60 fps) (aac)'
○ --edition=4 '18 - 640x360 (360p) muxed-11 (h264 30 fps) (aac 44100 Hz)'
○ --edition=5 '134 - 640x360 (360p) (h264 30 fps 281 kbps)'
○ --edition=6 '93 - 640x360 muxed-9 (h264 30 fps) (aac)'
○ --edition=7 '160 - 256x144 (144p) (h264 30 fps 111 kbps)'
○ --edition=8 '91 - 256x144 muxed-7 (h264 30 fps) (aac)'
● Video --vid=1 '299 - 1920x1080 (1080p60)' (h264 1920x1080 60 fps 3353 kbps) [default]
○ Audio --aid=6 '251 - audio only (medium)' (opus 48000 Hz 130 kbps)
● Audio --aid=7 '140 - audio only (medium)' (aac 44100 Hz 129 kbps) [default]
○ Audio --aid=8 '139 - audio only (low)' (aac 22050 Hz 48 kbps)
File tags:
Date: 20191121
Title: NEW SONG BACK2BACK | DANUCD SKINS | Danucd
Uploader: Danucd
Channel_URL: https://www.youtube.com/channel/UCsIiIEGRoBILi8LSkWNPqXA
[modernz] URL detected.
[modernz] Approximating file size...
[modernz] Executing: yt-dlp -f (bv*[vcodec~='^(av(0|c)1)']+ba[acodec^=mp4a])/b --no-download -O %(filesize,filesize_approx)s https://youtu.be/hrk8ZhjoB-Q
AO: [wasapi] 48000Hz stereo 2ch float
VO: [gpu-next] 1920x1080 yuv420p
[osd/libass] fontselect: Using default font family: (mpv-osd-symbols, 400, 0) -> ArialMT, 0, ArialMT
Cache dumping started.
[ffmpeg] mp4: track 1: codec frame size is not set
[recorder] This is an experimental feature. Output files might be broken or not play correctly with various players (including mpv itself).
[recorder] Discontinuity at timestamp 0.000000.
Cache dumping successfully ended.
[modernz] Download size: 31.91 MiB
Exiting... (Quit)

Output file 1MiB and not playable
warning [ffmpeg] mp4: track 1: codec frame size is not set

Log File

output.txt

Sample Files

No response

I carefully read all instruction and confirm that I did the following:

• I tested and confirmed that the issue exists with the latest release version or newer.
• 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.

[guidocella]

#17936 fixes this for the initially selected video track. It still doesn't work after changing it which requires the proposal in #17936 (comment).

[Rochkiller]

@guidocella, I tried the artefact : it broke everything !!! :@

mpv --version

mpv v0.41.0-dev-g6efd35fa3 Copyright © 2000-2026 mpv/MPlayer/mplayer2 projects
built on May 17 2026 18:58:42
libplacebo version: v7.364.0
FFmpeg version: bbdf847
FFmpeg library versions:
libavcodec 62.28.100
libavdevice 62.3.100
libavfilter 11.14.100
libavformat 62.12.100
libavutil 60.26.100
libswresample 6.3.100
libswscale 9.5.100

mpv https://youtu.be/hrk8ZhjoB-Q

[auto_profiles] Applying auto profile: youtube
[osd/libass] fontselect: Using default font family: (mpv-osd-symbols, 400, 0) -> ArialMT, 0, ArialMT
Not seekable, but enabling seeking on user request.
No protocol handler found to open URL https://rr4---sn-25glenlz.googlevideo.com/videoplayback?[...]%3D
The protocol is either unsupported, or was disabled at compile-time.
EDL: Could not open source file 'https://rr4---sn-25glenlz.googlevideo.com/videoplayback?[...]%3D'.
No video or audio streams selected.
Exiting... (Errors when loading file)

mpv https://kick.com/theburntpeanut

[auto_profiles] Applying auto profile: kick
No protocol handler found to open URL https://kick.com/theburntpeanut
The protocol is either unsupported, or was disabled at compile-time.
[osd/libass] fontselect: Using default font family: (mpv-osd-symbols, 400, 0) -> ArialMT, 0, ArialMT
Not seekable, but enabling seeking on user request.
No protocol handler found to open URL https://fa723fc1b171.euw33.playlist.live-video.net/v1/playlist/[...]P.m3u8
The protocol is either unsupported, or was disabled at compile-time.
EDL: Could not open source file 'https://fa723fc1b171.euw33.playlist.live-video.net/v1/playlist/[...].m3u8'.
No video or audio streams selected.
Exiting... (Errors when loading file)

[guidocella]

You can try the modified ytdl_hook.lua without the artifact.

[Rochkiller]

Sorry but I lose me here.
I searched ytdl_hook.lua on my computer and didn't find it.

So I retrieved this file : https://github.com/mpv-player/mpv/blob/master/player/lua/ytdl_hook.lua
Put it in my scripts folder
Did this modification : #17936 (comment)

Did I do the right thing ?

• If yes, that didn't solve my issue
• If no, please give me instructions

[guidocella]

You also need --ytdl=no.

[Rochkiller]

I added print("DEBUG: ytdl_hook.lua loaded") at end of script to confirm its loading
Outfile 0KiB and got this error :

[recorder] Can't mux one of the input streams.
Cache dumping stopped due to error.

mpv --ytdl=no https://youtu.be/hrk8ZhjoB-Q

[ytdl_hook] DEBUG: ytdl_hook.lua loaded
[auto_profiles] Applying auto profile: youtube
[osd/libass] fontselect: Using default font family: (mpv-osd-symbols, 400, 0) -> ArialMT, 0, ArialMT
Not seekable, but enabling seeking on user request.
● --edition=0 '299 - 1920x1080 (1080p60) (null 60 fps 3353 kbps)'
○ --edition=1 '301 - 1920x1080 muxed-14 (null 60 fps) (null)'
○ --edition=2 '298 - 1280x720 (720p60) (null 60 fps 1605 kbps)'
○ --edition=3 '300 - 1280x720 muxed-12 (null 60 fps) (null)'
○ --edition=4 '18 - 640x360 (360p) muxed-11 (null 30 fps) (null 44100 Hz)'
○ --edition=5 '134 - 640x360 (360p) (null 30 fps 281 kbps)'
○ --edition=6 '93 - 640x360 muxed-9 (null 30 fps) (null)'
○ --edition=7 '160 - 256x144 (144p) (null 30 fps 111 kbps)'
○ --edition=8 '91 - 256x144 muxed-7 (null 30 fps) (null)'
● Video --vid=1 '299 - 1920x1080 (1080p60)' (null 1920x1080 60 fps 3353 kbps) [default]
○ Audio --aid=6 '251 - audio only (medium)' (null 48000 Hz 130 kbps)
● Audio --aid=7 '140 - audio only (medium)' (null 44100 Hz 129 kbps) [default]
○ Audio --aid=8 '139 - audio only (low)' (null 22050 Hz 48 kbps)
File tags:
Date: 20191121
Title: NEW SONG BACK2BACK | DANUCD SKINS | Danucd
Uploader: Danucd
Channel_URL: https://www.youtube.com/channel/UCsIiIEGRoBILi8LSkWNPqXA
[modernz] URL detected.
[modernz] Approximating file size...
[modernz] Executing: yt-dlp -f (bv*[vcodec~='^(av(0|c)1)']+ba[acodec^=mp4a])/b --no-download -O %(filesize,filesize_approx)s https://youtu.be/hrk8ZhjoB-Q
AO: [wasapi] 48000Hz stereo 2ch float
VO: [gpu-next] 1920x1080 yuv420p
[osd/libass] fontselect: Using default font family: (mpv-osd-symbols, 400, 0) -> ArialMT, 0, ArialMT
Cache dumping started.
[recorder] Can't mux one of the input streams.
Cache dumping stopped due to error.
[modernz] Download size: 31.91 MiB
AV: 00:00:07 / 00:01:17 (10%) A-V: 0.000 Cache: 69s/32MB
Exiting... (Quit)

[guidocella]

That is strange mpv --no-config https://youtu.be/hrk8ZhjoB-Q and dump-cache works for me with or without my PR. It seems the video codec is null in your case for some reason. Try updating yt-dlp.

[Rochkiller]

I'm already on latest version

yt-dlp -U

Latest version: stable@2026.03.17 from yt-dlp/yt-dlp
yt-dlp is up to date (stable@2026.03.17 from yt-dlp/yt-dlp)

How did you dump-cache with no-config mpv ?

[guidocella]

dump-cache 0 9 /tmp/foo.mkv

[Rochkiller]

So, here what I did :

input file created : mykeys.conf
d dump-cache 0 9 C:/tmpvideo.mp4

mpv --no-config --input-conf="C:/Program Files/mpv/mykeys.conf" https://youtu.be/hrk8ZhjoB-Q

● --edition=0 '299 - 1920x1080 (1080p60) (h264 60 fps 3353 kbps)'
○ --edition=1 '301 - 1920x1080 muxed-14 (h264 60 fps) (aac)'
○ --edition=2 '298 - 1280x720 (720p60) (h264 60 fps 1605 kbps)'
○ --edition=3 '300 - 1280x720 muxed-12 (h264 60 fps) (aac)'
○ --edition=4 '18 - 640x360 (360p) muxed-11 (h264 30 fps) (aac 44100 Hz)'
○ --edition=5 '134 - 640x360 (360p) (h264 30 fps 281 kbps)'
○ --edition=6 '93 - 640x360 muxed-9 (h264 30 fps) (aac)'
○ --edition=7 '160 - 256x144 (144p) (h264 30 fps 111 kbps)'
○ --edition=8 '91 - 256x144 muxed-7 (h264 30 fps) (aac)'
● Video --vid=1 '299 - 1920x1080 (1080p60)' (h264 1920x1080 60 fps 3353 kbps) [default]
○ Audio --aid=6 '251 - audio only (medium)' (opus 48000 Hz 130 kbps)
● Audio --aid=7 '140 - audio only (medium)' (aac 44100 Hz 129 kbps) [default]
○ Audio --aid=8 '139 - audio only (low)' (aac 22050 Hz 48 kbps)
File tags:
Date: 20191121
Title: NEW SONG BACK2BACK | DANUCD SKINS | Danucd
Uploader: Danucd
Channel_URL: https://www.youtube.com/channel/UCsIiIEGRoBILi8LSkWNPqXA
AO: [wasapi] 48000Hz stereo 2ch float
VO: [gpu-next] 1920x1080 yuv420p
Cache dumping started.
[ffmpeg] mp4: track 1: codec frame size is not set
[recorder] This is an experimental feature. Output files might be broken or not play correctly with various players (including mpv itself).
[recorder] Discontinuity at timestamp 0.000000.
Cache dumping successfully ended.
AV: 00:00:10 / 00:01:17 (13%) A-V: 0.000 Cache: 66s/30MB
Exiting... (Quit)

Even if Cache dumping successfully ended., output file is too small (163KiB)

For Kick live stream, got this error (output file empty 0KiB) :

[ffmpeg] mp4: sample rate not set
[recorder] Writing header failed.
Cache dumping stopped due to error

Tried with mkv, same happen :

[ffmpeg] matroska: sample rate not set
[recorder] Writing header failed.
Cache dumping stopped due to error