Are you trying to in a specific app (like Unity or FFmpeg)?
If you are recording live streams to MP4, Issue #382 on the deals with recording failures. 382 mp4
To join two MP4 files where one lacks audio, use FFmpeg to merge the streams without re-encoding to save time. To give you a better "text," could you let me know: Are you trying to in a specific app (like Unity or FFmpeg)
Videos may fail to play or crash using the default DirectShow filter. Solutions: 382 mp4
Force use of if you prefer staying with DirectShow. ✍️ Text Overlays (Mobile-FFmpeg)
If you've downloaded an MP4 on an iPhone and can't find it, check the Downloads folder within the Files app .