[FFmpeg-user] co64 atom in QT / Mp4, and compatibility with Premiere _ FIXED

[Bouke]

> On 31 Jan 2021, at 13:06, Bouke <bouke at editb.nl> wrote:
> 
> This is not an FFmpeg question perse, but I hope someone knows more about atoms than I do.
> 
> Similar to the previous thread, I am modifiying clips ‘in place / destructive’. (For .Mp4 / .mov files)
> 
> For that I re-write or re-order the moov atom to needs.
> That all seems to work fine, if files are < 4 gig.
> On larger files, when I want to change TC, I add an mdat atom with the TC converted to frame number.
> In the TC track (That I rip from a dummy FFmpeg short transcode), I change the pointer in the TC tracks stco atom to the newly added mdat location.
> So far so good.
> 
> Now, when the new mdat pos goes over 4 gig, I add an co64 atom so I have 8 bytes to set it, and I  change the whole shebang to reflect the new length of all atoms in the structure.
> This also ‘sorta kinda’ works, as QT player displays the correct TC.
> 
> BUT, Adobe Premiere does NOT like this, it gives me another TC that I can’t place for the life of me…
> If I omit the co64 atom and find ‘some’ spot (either inside an mdat atom or not), it works, but it seems Premiere totally ignores the co64 info.

For the archives:
Fixed. trouble was that Premiere / Resolve expect the co64 atom INSTEAD of stco, rather than after to overwrite previous value.

Bouke