[xiph-rtp] Updated Vorbis and new Theora I-D's

[Ralph Giles]

On Tue, Feb 01, 2005 at 04:36:40AM +0000, Phil Kerr wrote:

> I've just checked into svn two new documents.

Great to see these!

> I've included a MIME section for the packed headers.  I'm not 100% sure 
> if the media type is right, should it be audio or application?

Hmm. I guess we need a separate format for multicast.

For reliable transmission, what do you think about just serving an Ogg
file with all the headers embedded normally (and the actual compressed
data elided)? This is the simplest approach programmatically.

Have you thought about including the CRC32 in the packed header format?
That might also add some convenience, and help verify both intended
match and successful transmission in lossy delivery schemes.

> Also included is details on generating the crc32 hash, with it's 
> polynomial and C code fragment.

Yay. I'd also reference it, indicating (for example) if it's the same
hash used by Ogg or zlib, just to save people checking the definition
by hand.

> A new I-D covering the RTP transportation of Theora Video is available.  
> It draws heavily from the Vorbis draft and shares a lot of the basic ideas.

One quick thing: the three 'total number of blocks' aren't actually in the
setup header; they're calculated from the other fields that are in the 
bitstream. What looks like the packet structure table in the spec is
actually the output of the specified decode routine, which generates the
redundant values for the convenience of other sections of the spec.

I'd also suggest some wording clarification:

    'width/height of the encoded frame in...'
    'width/height of the valid picture region...'

And reference the definitions in the spec since these informative but
not nominal.

KFGSHIFT would better be defined as the log of the maximum keyframe spacing,
since the granulepos is irrelevent in this context.

Technically, the NOMBR, QUAL, and KFGSHIFT are not necessary for decode
and could be elided. Reasonable values can be recomputed by an application
that needs to regenerate the original theora packet. In practice, including
them probably does no harm.

 -r