MediaConvert cannot handle input video recorded in Safari Media Recorder

Question

We noticed an issue with MediaConvert when we provide an input file that comes from Safari Media Recorder API (https://developer.mozilla.org/en-US/docs/Web/API/MediaRecorder).  Apparently Safari records these as a "fragmented mp4" (mp4 file with multiple moov/moof/mdat markers).

MediaConvert doesn't fail, but the output video it produces is very jerky/stuttery and it seems to be incorrectly interpreting the source frame rate, and duplicating frames to provide a jerky output video.

If we run the problem input file through a local FFMPEG stream copy command first:

```
ffmpeg -i safari_recorded_file.mp4 -c copy stream_copy.mp4
```
and then supply the `stream_copy.mp4` file as the input to MediaConvert, it does work as expected.

However, this extra step of having to run ffmpeg on a local machine is not desirable, since we're trying to use MediaConvert for this!

Has anyone run into this, or have a better workaround?  Thanks.

Answer

Reposting this answer.
@boast-kevin, can you indicate if the Safari Media Recorder was producing variable frame rates (VFR) or constant frame rates (CFR)? Certain configurations of VFR may cause the issues you are experiencing. Would you be able to provide the version of the OS and the Safari Recorder? Also, are you able to provide an example file that has this issue?

MediaConvert cannot handle input video recorded in Safari Media Recorder

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