[FFmpeg-user] Unsophisticated user has a question

[Reindl Harald]

Am 11.08.2013 14:39, schrieb ffmpeg at riventree.com:
> I've encountered something that makes me suspicious that I've lost data. I
> have a .MOD file (Grrr Cannon vidcams) that takes up 39M of storage. I
> converted it to .mp4 with the simplest possible command:

you *always* lose data with non-lossless codecos at any conversion
any time, always, that's how things are working as you always lose
data when change a jpeg image and save it again

> jde-desktop% ffmpeg -i 002.MOD 002.mp4
> And the resultant .mp4 is 9.9M!

nothign special

> A cursory (and uninformed) glance at the output shows a [720x480 / yuv420p
> / 29.97fps] stream in and the same thing out. The video input is
> "mpeg2video" and the output is "libx264", the audio is AC3 in and AAC out.
> 
> *I need to know if that's just better packing or (this is the problem) I've
> lost data in the conversion.*

http://en.wikipedia.org/wiki/MPEG-2
http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC

> Can anyone explain the 4x size difference with the data there?

it is logical from MPEG3 to H264

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