[FFmpeg-user] "-acodec copy -vcodec copy" output smaller than original

Bertram Lyons bertram at avpreserve.com
Fri Sep 16 20:37:45 EEST 2016

> On Fri, Sep 16, 2016 at 05:25:07 +0000, Olexandr Melnyk wrote:
> > ffmpeg -i Svalbard2016_g04033.mp4 -acodec copy -vcodec copy -map 0
> > output.mp4
> >
> > Here, the output file I'm getting is 5MB smaller than the source file.
> And
> > if I do the same for a bigger source file, the size difference is bigger
> as
> > well.
> > Any thoughts why this is happening?

> > I'm going to delete the source files eventually, hence I'm afraid if I'm
> > losing anything (metadata?) in the process.
> > https://dl.dropboxusercontent.com/u/30369146/Svalbard2016_g04033.mp4
> (produced
> > with an original SJ5000+ camera, if that's of any help)
Hi Olexandr --

>From a quick look at your source file, I'd say ffmpeg is dropping the
approximately 5MB of "free" 00s that are at the end of your source file.
Take a look in a hex viewer at your source file and you will see a "free"
atom with almost 5MB of 00s at the end of the file.

Best --


Bertram Lyons, CA

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