getSafParameterForWrite doesn't work with -movflags faststart on Android

[gazlaws-dev]

Description
Creating an output video (.mp4) with the-movflags faststart doesn't work with getSafParameterForWrite (using Android's Storage Access Framework), presumably because it's not able to read the file for the second pass.

Expected behavior
An option to create the output file with read and write permissions. Maybe getSafParameter can be made public so we can pass 'rw' as openMode.

Current behavior
Output file is not created properly, error shown:

2021-10-03 15:27:24.849 24442-24657/x I/ffmpeg-kit: Output #0, mp4, to 'saf:105.mp4':
2021-10-03 15:27:28.770 24442-24657/x E/ffmpeg-kit: Error writing trailer of saf:105.mp4: Bad file descriptor

To Reproduce

inputVideoUrl = FFmpegKitConfig.getSafParameterForRead(requireContext(), inputVideoUri);
outputFilePath = FFmpegKitConfig.getSafParameterForWrite(requireContext(), resultVideoUri);

ffmpeg command (shortened):
  -y -i "saf:90.mp4" -vcodec libx264  -movflags faststart  saf:105.mp4

Logs

2021-10-03 15:27:18.726 24442-24442/x I/EditFragment: getContent: Input video absolute file path: saf:90.mp4
2021-10-03 15:27:24.547 24442-24657/x I/ffmpeg-kit: Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'saf:90.mp4':
2021-10-03 15:27:24.849 24442-24657/x I/ffmpeg-kit: Output #0, mp4, to 'saf:105.mp4':
2021-10-03 15:27:28.770 24442-24657/x E/ffmpeg-kit: Error writing trailer of saf:105.mp4: Bad file descriptor

Environment

• Platform: Android
• Architecture: arm64-v8a
• Version: v4.5

[tanersener]

Thanks for reporting this issue. Yeah, it seems like there is a problem there. Existing flags used internally ("r" and "w") are not enough to move the moov atom to the beginning of the file. We need to provide another method for it.