[FFmpeg-user] Preserving 'udta' atom when using -movflags +faststart

Carl Eugen Hoyos ceffmpeg at gmail.com
Tue May 1 23:50:10 EEST 2018

2018-05-01 22:35 GMT+02:00, Julian Cooper <youcanreachjulian at gmail.com>:

> I'm using the ffmpeg CLI to pre-process AVC and HEVC MP4s. Part of that
> pre-processing involves moving the 'moov' atom to the head of the MP4. The
> 'moov' atom contains a 'udta' with metadata I would like to preserve. The
> 'moov/udta' atom is being dropped when calling:
> ffmpeg -i source.mp4 -c copy -movflags +faststart faststart.mp4

You misunderstand:
This command does not take an mp4 file and move its atoms
around. It reads an mp4 file and writes a new mp4 file with
many different attributes.
The tool you need is qt-faststart which is also part of the
FFmpeg project.

Carl Eugen

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