[FFmpeg-user] ProRes Quicktimes with audio not playing back reliably

[Tim Nicholson]

On 16/10/12 19:17, Bob Maple wrote:
> Still trying to get this one solved.  I'd been working off-list with
> Thomas Worth and here's what we've discovered so far.
> 
> Using "ffprobe -show_packets" on ProRes files made by ffmpeg and ones
> made on a Mac under Final Cut or even files directly from the ARRI Alexa
> camera, it seems that ALL "proper" FCP ProRes Quicktimes are 16-bit
> aligned;  That is, every audio and video packet seems to be an even
> length, and the offsets are on even bytes.  Files generated by ffmpeg
> wind up about 25% odd-length and thus cause subsequent un-alignment.
> 
> This seems like a possible likely reason for the odd performance issues,
> with the inconsistent behavior of dropped frames.  I don't know if
> Quicktime specifies any sort of alignment, as other files generated by
> Quicktime Pro its self in other codecs don't seem to be strictly
> aligned;  but I've run dozens of "proper" ProRes files through ffprobe

I wonder if "other codecs" are fixed frame size? Or to put it another
way Prores is kind of DNX++. DNX is fixed frame size, which helps
seeking, and prores has a small amount of variability. I wonder if
genuine prores adds the above constraint to help seek-ability which has
been missed in the reverse engineering.


> [...


-- 
Tim