[vorbis-dev] Ogg as container format
kmarks at apple.com
Thu Sep 27 18:22:44 PDT 2001
At 8:34 PM +1000 9/26/01, Michael Smith wrote:
>rm goal is for ogg to be a generic media container format in
>the same way as riff (avi/wav), qt, and so on are. Except better,
OK, I'll bite. Better how? What is bad about QT? How is Ogg better?
IFF-like formats have stood up very well over time because of the
future compatibility built-in (the behaviour for unknown chunks is
QT's structure was picked up by the MPEG4 committee because of this robustness.
QT defines the structure of a particular movie independently of the
data - you can gain enough information to seek anywhere in the file
by reading this movie header from the front. In fact, this header can
be completely independent of the media data, which is how QT is able
to import so many other formats.
From what I can see of Ogg, everything is down in the stream
structure, and the lacing values used for packet framing will
introduce a lot of overhead for packets bigger than 1024 bytes.
What is the point of making packets and pages independent, and having
two parallel framing structures going on at once, with the
concomitant problem of having to slice and dice the whole time?
You're going to have big trouble getting DV or uncompressed video
into this structure. Dv frames are 120000 bytes for NTSC and 144000
for PAL. They are all the same size. To put these in Ogg you need 471
& 565 lacing values per frame, and you need to add up these bytes to
get the constant length.
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