AWS Media Convert removes silent audio which causes the output video to be severly out-of-sync with audio

Hi re:Post community,

We have been using AWS Elemental MediaConvert for about 3 years but we have encountered some very strange behaviour roughly from the 10th of December 22 onwards. MediaConvert started removing all of the silent audio from our audio inputs and it merges all the speech in the input together. This is causing major syncing issues between the video and the audio in the output file.

The rough specification of our MediaConvert jobs is:

• video input: H.264 or VP8
• audio input: Matroska with OPUS
• output: MPEG-4 AVC (H.264)

We started receiving customer reports on the 12th of December saying that their videos are out of sync. I found a job from 9 Dec that was OK and I cloned and reran the job today (19 Dec). The result from today was missing all the silent audio which was matching all the broken files reported by our customers. The two jobs are using exactly the same inputs and the same configuration.

This makes me think something must've changed internally in MediaConvert that is causing these issues. Perhaps a new setting?

Has anyone experienced the same?

Thanks Michal