Recorded video file has no duration

[Xennis]

Describe the bug

Recording videos have no duration. The video file of a recording can be played but has no duration. This causes trouble with video applications.

My guess is it's due to https://github.com/muaz-khan/RecordRTC/issues/147 . The authors added a way to fix it: https://github.com/muaz-khan/RecordRTC/issues/147#issuecomment-459954869

Minimal reproduction

Steps to reproduce the behavior:

1. Run slidev --open
2. Open the slides
3. Start a recording.
4. Stop the recording and save the file.
5. Check if the file has a duration, e.g.
   • open it with VLC player and see the bar shows no proper duration
   • or use in the shell ffprobe -i <my-file-here> -show_entries format=duration -v quiet -of csv="p=0". It will print N/A instead of a duration

Environment

• Slidev version: 0.49.29
• Browser: Chrome (128.0.6613.113) and Firefox (125.0.2)
• OS: Ubuntu

[Xennis]

A manual workaround:

ffmpeg -i my-recording.mp4 -c my-recording-copy.mp4