[FFmpeg-devel] FFV1 Specification
michaelni at gmx.at
Sun Apr 8 15:16:20 CEST 2012
On Sun, Apr 08, 2012 at 02:45:45PM +0200, Michael Niedermayer wrote:
> On Sun, Apr 08, 2012 at 02:36:55PM +0200, Michael Niedermayer wrote:
> > On Sun, Apr 08, 2012 at 02:21:38PM +0200, Peter B. wrote:
> > > On 04/08/2012 01:58 PM, Michael Niedermayer wrote:
> > > > Its unlikely that decoding a damaged frame will have the end-of-stream
> > > > matching with the end of the pixels. So id say 99% of the damaged
> > > > frames should be detectable that way. Detection failure should become
> > > > a problem though when the error is close to the end of the frame.
> > > > Adding a checksum should be no problem, that can be done.
> > > Just to avoid confusion on my side:
> > > The word "frame" here applies to a video-frame or something like a
> > > data-frame inside the bitstream?
> > video frame, yes
> > >
> > >
> > > >> 2) Can you decode the next frame. Since FFV1 does not specify the
> > > >> container, that is not a property of FFV1. If you store it in e.g.
> > > >> NUT the answer is "better than with any MPEG-format", if you would store
> > > >> it in mov/mp4 the answer would be "about the same as for e.g. Intra-only H.264"
> > > >> I'd say.
> > > > yes but dont forget ffv1 can reuse range coder contexts over frames
> > > > so one has to set the gop size to 1 if this kind of next frame recovery
> > > > is important to them
> > > >
> > > Interesting to hear that.
> > > These are exactly the "small details" which I'd love to find when
> > > reading docs about FFv1 :)
> > > I thought that when using an intra-frame-only codec, all frames are
> > > self-contained and there'd be no GOPs. Am I getting something wrong here?
> > they are intra frames in the sense that there is no motion
> > compensation. The previous frame(s) also dont need to be kept as
> > reference frames, but the contexts can be reset once per frame or
> > less often to improve compression performance
> > The ffv1 spec does mention this:
> > Initial values for the context model
> > At keyframes all range coder state variables are set to 128
> > this implicates that no keyframe -> no reset
> but reading this again, this should be written in a more direct way
> because as is its easy to miss it.
> maybe you could suggest some text ?
Also in relation to this (10 seconds from the matrix lobby scene)
using rangecoding and the larger context model:
ffv1 GOP=300 23736978
ffv1 GOP=1 25056734
ffv1.2 GOP=300 23648224
ffv1.2 GOP=1 23645074
and ffv1.2 does low latency multithreaded encoding & decoding for all
who dont know that yet ...
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
I am the wisest man alive, for I know one thing, and that is that I know
nothing. -- Socrates
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