transmuxing MP4 recording output is broken

[iameli]

Describe the bug
Production of MP4 files from recordings is broken.

To Reproduce
Steps to reproduce the behavior:
0. Check out a branch that includes fixes for object-store-without-API functionality: #2477

1. Run go-livepeer with livepeer -broadcaster -recordStore s3+https://GOOGAMT7AUXJ2SXGAGRI4NQI:[redacted-but-i-can-give-you-it]@storage.googleapis.com/go-livepeer-vod-test
2. Run curl http://localhost:8935/recordings/stream%2Bcountdown-Yg3OEth7/source.mp4
3. You will get an empty file back, zero bytes.

We ran a bisect of go-livepeer and it appears that the first bad commit was 9324731 cc @AlexKordic

Logs:

ERROR: decoder.c:308] demuxer: Unable to open input : Invalid data found when processing input
E0627 11:16:35.515189   55340 ffmpeg.go:924] Transcoder Return : Invalid data found when processing input
E0627 11:16:35.515284   55340 mediaserver.go:1246] Error transmuxing to mp4 request=http://localhost:8935/recordings/stream%2Bcountdown-Yg3OEth7/source.mp4 uri=https://storage.googleapis.com/go-livepeer-vod-test/stream+countdown-Yg3OEth7/longos.local/source/0.ts manifestID=stream+countdown-Yg3OEth7 err="Invalid data found when processing input"
I0627 11:16:35.515378   55340 mediaserver.go:1188] Completed mp4 request=http://localhost:8935/recordings/stream%2Bcountdown-Yg3OEth7/source.mp4 manifestID=stream+countdown-Yg3OEth7 sourceBytes=322608 destBytes=0

[gioelecerati]

acaudwell/Gource#216
h2soong/m3u8_To_MP4#10