Re: [MMUSIC] [AVTCORE] Question - Erratum 4097

[[e-mail] (Dale R. Worley)]

Julius Friedman <[e-mail]> writes:
> The RFC only provided a way for certain sized images much lower then what
> JPEG supports to be transferred, this erratum fixes this by specifying that
> in some cases you may need to use a different fraction to obtain the height
> (which might not be in a multiple of 16 anyway) additionally it allows one
> to deal with the nuance that if the data is so large that the
> FragmentOffset will probably overflow during this time and provides a way
> to deal with that as well.

Whew, you're going to have to slow down here.  I'm not tracking what you
say very well, but if I read it correctly, you're saying you want to
change the divisor in sections 3.1.5 and 3.1.6 from 8 to 256.  Is that
really correct?  And your justification seems to be that there are JPEGs
that are so large that their sizes can't be represented within an 8 bit
field with a multiplier of 8 (i.e., >2048).

If so, this isn't an erratum, but a technical change, and it would have
to go through the working group as an update to the RFC.  It would also
be incompatible with every implementation that now uses this feature.

In regard to "Fragment Offset", you seem to be allowing for JPEGs in
excess of 2^24 bytes, which seems to me to be unlikely within the
constraints of the existing height and width limitations.  In any case,
reducing Fragment Offset modulo 2^24 would make reassembly of large
frames ambiguous -- you'd really need a larger Fragment Offset field.

What you're really asking for here is an RTP payload format much like
RFC 2435 but different from it and incompatible with it.  That would be
a new piece of work, as well as requiring assignment of a new "encoding
name" so that control protocols could specify it.  (The "JPEG" encoding
name is assigned to RFC 2435 media by RFC 3551 section 5.2.)

Errata aren't for situations where "I think this protocol could have
been designed better", but where the *text* doesn't express what the
working group *meant*.

Dale