[NUT-devel] [nut]: r613 - docs/nutissues.txt

[Michael Niedermayer]

On Tue, Feb 12, 2008 at 07:37:53PM +0100, Alban Bedel wrote:
> On Tue, 12 Feb 2008 17:57:03 +0100
> Michael Niedermayer <michaelni at gmx.at> wrote:
> 
> > On Tue, Feb 12, 2008 at 05:47:13PM +0100, Alban Bedel wrote:
> > > On Tue, 12 Feb 2008 16:00:10 +0100 (CET)
> > > michael <subversion at mplayerhq.hu> wrote:
> > > 
> > > > Modified: docs/nutissues.txt
> > > > ==============================================================================
> > > > --- docs/nutissues.txt	(original)
> > > > +++ docs/nutissues.txt	Tue Feb 12 16:00:09 2008
> > > > @@ -162,3 +162,8 @@ How do we identify the interleaving
> > > >  A. fourcc
> > > >  B. extradata
> > > 
> > > I would vote for this with a single fourcc for pcm and a single
> > > fourcc for raw video. Having infos about the data format packed in
> > > the fourcc is ugly and useless. That just lead to inflexible lookup
> > > tables and the like. 
> > 
> > > Instead we should just define the format in a way similar to what
> > > mp_image provide for video (colorspace, packed or not, shift used
> > > for the subsampled planes, etc). That would allow implementations
> > > simply supporting all definable format, instead of a selection of
> > > what happened to be commonly used formats at the time the
> > > implementation was written.
> > 
> > The key points here are that
> > * colorspace/shift for subsampled planes, etc is not specific to RAW,
> > its more like sample_rate or width/height
> 
> Sure, but when a "real" codec is used, it's the decoder business to tell
> the app what output format it will use. NUT can provide infos about the
> internal format used by the codec, 

Only very few codecs have headers which store informations about things like
shift for subsampled planes. Thus if this information is desired it has to
come from the container more often than not. If its not desired then we also
dont need it for raw IMHO.


> that would help dealing with decoder
> including slow colorspace conversions.

I have no interrest in supporting or helping this case, and i suspect iam not
alone here.


> But that's definitly
> non-essential information, any player should be able to do without it.
> 
> However for RAW data the "decoder" need to know the exact format used,
> just like some other decoder need some huffman tables or whatever.
> And the logical place for such information is the extradata imho.

see above, also there really are 2 things
1. How things are stored (packed vs. planar, the precisse byte packing, ...
2. What is stored (colorspace details YUV BT123 vs BT567, chroma shift,
   channel positions

1. defines the format that is packing of raw bytes this is somehow similar
   to mpeg4 vs h261 thus i think it should be specified by the fourcc
2. is needed for non raw as well which makes fourcc and extradata unuseable


[...]
> 
> > > 
> > > >  C. New field in the stream header
> > > > +D. Only allow 1 standard interleaving
> > > > +
> > > > +What about the interleaving of non raw codecs, do all specify the
> > > > +interleaving, or does any leave it to the container? If so, our
> > > > options +would be down to only C.
> > > 
> > > On a related subject, it might also be useful to define the channel
> > > disposition when there is more than one. Mono and stereo can go by
> > > with the classical default, but as soon as there is more channels
> > > it is really unclear. And imho such info could still be usefull
> > > with 1 or 2 channels. Something like the position of each channel
> > > in polar coordinate (2D or 3D?) should be enouth.
> > 
> > I agree
> > What about that LFE channel thing?
> 
> I was thinking about simply setting the distance to 0, however a flag
> for "non-directional" channels might be better.

This is wrong, LFE is not about direction but about the type of speaker.
LFE stands for "Low-frequency effects".
If id move a other random speaker at disatnce 0 and the LFE one out and
switch channels it wont sound correct ...


> 
> > And where do we put this info, The stream header seems the logic
> > place if you ask me ...
> 
> I agree, this is essential information for proper presentation it
> definitly belong there.

Good, now we just need to agree on some half sane way to store it.
for(i=0; i<num_channels; i++){
    x_position                  s
    y_position                  s
    z_position                  s
    channel_flags               v
}

CHANNEL_FLAG_LFE             1

seems ok?


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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