[FFmpeg-user] Any way to estimate moov_size in mov/mp4?

Carl Zwanzig cpz at tuunq.com
Fri Feb 10 22:40:43 EET 2023

On 2/10/2023 3:20 AM, Bouke / Videotoolshed wrote:
> Faststart is for internet / network playing only, when the entire file is not yet available.

Not only for network playback; maybe often used for that but there's no 
reason to limit the use.

> If movflags faststart is needed, it should be darn fast as your files
> ’should’ be fairly small, as they are intended for (relative) low
> bandwith. > There is NO penalty for having the MOOV atom at the end if a file is
> local, as parsing all atoms will not take longer than a few secs if the
> file is local.
It's difficult to characterize a 2 hour FHD (or 4k) video file as small or 
intended for low bandwidth, and there -is- a penalty ("a few seconds"). Many 
playout servers will play from MP4 files and "a few seconds" is a few too 
long when a specific file is to play. Some software will pre-open the file 
and start it on time, but that's no reason to not put the necessary info at 
the head of the file. (The OP also says "As the produced files are very big 
anyway I don't mind wasting a few MB by overestimating.")

It would be interesting to see how accurate Bouke's technique is for 
estimating the moov atom size; probably close enough but confirmation is 
always good.



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