[FFmpeg-devel] [PATCH] ffv1enc: Make ffv1.3 non experimental

Michael Niedermayer michaelni at gmx.at
Sat Aug 17 20:00:33 CEST 2013

On Sat, Aug 17, 2013 at 03:27:43PM +0200, wm4 wrote:
> On Sat, 17 Aug 2013 13:33:27 +0200
> Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Sat, Aug 17, 2013 at 08:27:14AM +0200, Reimar Döffinger wrote:
> > > On 17.08.2013, at 05:00, Michael Niedermayer <michaelni at gmx.at> wrote:
> > > 
> > > > The fate tests change as they used 1.2 previously
> > > 
> > > It's fairly minimal, but is it expected that every single frame becomes larger?
> > 
> > 1.3 adds 32bit CRCs per slice by default (can be disabled),
> > it adds slice headers to allow decoding one slice without the others
> > an additional slice size field is added to make it possible to find
> > slices within corrupted surroundings.
> > 
> > these add up to about 57bit per slice more
> > at 50 frames and 4 slices thats 1425 byte which comes close to the
> > actual difference, so i would say that explains the difference
> I'm just curious: isn't CRC a pretty slow checksum algorithm?

compared to what ?
md5 sha1, ... are all much slower
adler32 is faster but its pretty crap
murmur might be faster but it lacks many properties that crcs have,
and which may be important for error detection

> Why are
> checksums needed at all,

they arent "needed" but some users want to know which parts of a video
is undamaged and which are damaged with more certainity than what
you get by checking for decoder errors.

> isn't that the responsibility of the
> container, if it should be inside the file at all?

containers generally dont provide such checksums, even less so at
slice level. 

PS: if you have ideas for improving it, its certainly possible to make
changes to it for 1.4 ...

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct answer.
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