ffmpeg.exec hangs forever without error when I try to resize a video, but only when using the multithreaded version, while using a Chromium based browser or Safari. No issues on Firefox.

[Boux]

Describe the bug If I try to resize a video, either with the -s param or something like -vf scale=-2:480, the execution will simply hang forever and never give an error, but only when using the core-mt version (umd). If I try with the single-threaded version (core), everything works fine

To Reproduce

• Use Google Chrome on macOS (similar things happen on Chromium on Linux)
• Go to the /apps/vanilla-app/public/transcode-mt.html file in this project
• Modify this line: await ffmpeg.exec(['-i', name, 'output.mp4']); to await ffmpeg.exec(['-i', name, '-filter:v', 'scale=-2:480', 'output.mp4']);
• It hangs
• Do the same modification to the non-mt html file
• It does not hang
• Same issue on Safari
• Everything works on Firefox, mt or non-mt

Expected behavior ffmpeg.exec should not hang and successfully encode the video, or at the very least give an error.

Logs Here are the logs (directly from ffmpeg.on("log" ...)

[FFmpeg] ffmpeg version 5.1.4 Copyright (c) 2000-2023 the FFmpeg developers
[FFmpeg]   built with emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.40 (5c27e79dd0a9c4e27ef2326841698cdd4f6b5784)
[FFmpeg]   configuration: --target-os=none --arch=x86_32 --enable-cross-compile --disable-asm --disable-stripping --disable-programs --disable-doc --disable-debug --disable-runtime-cpudetect --disable-autodetect --nm=emnm --ar=emar --ranlib=emranlib --cc=emcc --cxx=em++ --objcc=emcc --dep-cc=emcc --extra-cflags='-I/opt/include -O3 -msimd128 -sUSE_PTHREADS -pthread' --extra-cxxflags='-I/opt/include -O3 -msimd128 -sUSE_PTHREADS -pthread' --enable-gpl --enable-libx264 --enable-libx265 --enable-libvpx --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libopus --enable-zlib --enable-libwebp --enable-libfreetype --enable-libfribidi --enable-libass --enable-libzimg
[FFmpeg]   libavutil      57. 28.100 / 57. 28.100
[FFmpeg]   libavcodec     59. 37.100 / 59. 37.100
[FFmpeg]   libavformat    59. 27.100 / 59. 27.100
[FFmpeg]   libavdevice    59.  7.100 / 59.  7.100
[FFmpeg]   libavfilter     8. 44.100 /  8. 44.100
[FFmpeg]   libswscale      6.  7.100 /  6.  7.100
[FFmpeg]   libswresample   4.  7.100 /  4.  7.100
[FFmpeg]   libpostproc    56.  6.100 / 56.  6.100
[FFmpeg] Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input_1503edd15afe4f709ee5c8c782ca25dd.mp4':
[FFmpeg]   Metadata:
[FFmpeg]     major_brand     : isom
[FFmpeg]     minor_version   : 512
[FFmpeg]     compatible_brands: isomiso2avc1mp41
[FFmpeg]     encoder         : Lavf59.16.100
[FFmpeg]   Duration: 00:02:19.10, start: 0.000000, bitrate: 1929 kb/s
[FFmpeg]   Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1920x1080, 1729 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
[FFmpeg]     Metadata:
[FFmpeg]       handler_name    : VideoHandler
[FFmpeg]       vendor_id       : [0][0][0][0]
[FFmpeg]   Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 191 kb/s (default)
[FFmpeg]     Metadata:
[FFmpeg]       handler_name    : SoundHandler
[FFmpeg]       vendor_id       : [0][0][0][0]
[FFmpeg] Stream mapping:
[FFmpeg]   Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
[FFmpeg]   Stream #0:1 -> #0:1 (aac (native) -> aac (native))
(this is where it hangs)

Desktop

• macOS 13.3.1
• Chrome, Safari

Additional context If there are issues with reproducing the bug, I'm not against the idea of doing a video call and sharing my screen

[Boux]

Followup: for some crazy unexplained reason, after MUCH trial and error, if I add the params "-c:a", "copy", so something like await ffmpeg.exec(['-i', name, "-c:a", "copy", '-filter:v', 'scale=-2:480', 'output.mp4']);, everything works. No idea why, I'm just gonna do this, I'm glad it works and at this point I don't even care to know why, yes it's currently 4:30 am.

[0xJacky]

Same issue

[vayron]

0.12.5~0.12.10 same issue, the old version 0.11.5 work

[yafkari]

Hahahha the solution of @Boux really worked, I literally just added "-c:a", "copy" to the parameters and it started to process the input.

Before that I was just getting to the logging of the streams info like that:

(Using @ffmpeg/core-mt@0.12.6/dist/umd)

EDIT: Still have the issue when trying to do things like -i myfile.png myfile.webp though. (But jpg to webp worked)

EDIT2: While trying to convert an mp4 to avi without -c:v copy, it was still hanging forever even with the c:a copy trick. By setting manually c:v libx264 it started.