Fwd: Text on ffmpeg

[Berthold Stoeger]

Hi Willem,

On Wednesday, 12 September 2018 20:39:21 CEST Willem Ferguson wrote:

> When looking for the date/time of a video file, which EXIF attribute is
> used to get the time? Is it a UCT value?

To my knowledge Quicktime (mp4, mov, etc.) doesn't have EXIF in that sense. It 
consists of "atoms" (which amazingly can contain other atoms - no kidding) and 
we search for the "mdhd" (=media header) atom, from which we extract the 
timestamp and the duration. The timestamp is supposed to be in UTC (as seconds 
since 1.1.1904 - Apple time).

You *can* incorporate XMP data (https://de.wikipedia.org/wiki/
Extensible_Metadata_Platform) into such a file. If there is interest, I can 
have a look at how much work it would be to extract useful information from 
that. Since Qt has an, albeit dog-slow, XML parser it shouldn't be too hard.

For WMV files we use the "file properties object" in a similar way.

Not sure if these details answer your question...?

> I am messing with exiftool to alter some videos to have date/times that
> coincide with a dive in order to see the way the video is shown on the
> profile.

Which option do you use to modify the date? I'll try to see what it does.

Berthold