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RE: QT vs MPEG-4
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RE: QT vs MPEG-4



Hi,

I'll give a shot at some of your questions.

> -----Original Message-----
> From: Per Bergland [mailto:email@hidden]
> Sent: Thursday, December 06, 2001 9:14 AM
> To: email@hidden;
> email@hidden
> Subject: QT vs MPEG-4
>
>
> Are there any docs, papers or list dwellers that can answer
> the following
> (maybe very dumb but nevertheless interesting) questions:
>
> "The MP4 file format ... design is based on the QuickTime.
> format from Apple
> Computer Inc"
> (from http://mpeg.telecomitalialab.com/standards/mpeg-4/mpeg-4.htm)
>
> Does that mean that a QuickTime movie is a
> standards-compliant MPEG-4 file
> if it uses only codecs from the MPEG-4 standard? If yes, then is it an
> invalid MPEG-4 file if it uses other media codecs such as GIF
> or Sorenson?
>
> What about if the movie has refs to other files (the Alias Manager is
> probably not in the MPEG-4 spec) or has a compressed header
> (is zlib in the
> MPEG-4 spec?)?
>
> Vice versa, is an MPEG-4 media file automatically a QuickTime
> movie, or are
> there additions (it says "based on") that aren't supported by
> QuickTime?

The MP4 file format has the same syntax as the QT file format: atoms
containing atoms and so on. The basic QT atoms appear in MP4 (mdat, moov,
mvhd, trak, etc), and things such as hint tracks are there also. But then,
MP4 movie files also require additional atoms that you will not find in a QT
movie (iods - Initial Object Descriptor, for instance), and you will often
find extra tracks as well (Scene description, object description, etc). So
the answer to your question is: no, a QT movie is not an MP4 movie. And
vice-versa, a QT movie is not an MP4 movie, even if it uses the same codecs
(which it very well could).
The fact that the file format and structure is the same however, makes the
DSS an MP4 streaming server without any modification.

> Envivio's streaming MPEG-4 server is based on DSS, but their
> client (Real/QT
> plugin) does not route its data through QuickTime's
> RTP/reassembler - they
> use their own homerolled UDP connections (and a local file
> can't be exported
> since they seem to do drawing directly in DirectDraw and not by
> decompressing frames for QT to render).
> Based on the license for DSS, one could assume that the
> MPEG-4 streaming
> capabilities in DSS 4 comes partly from Envivio's work (or
> the other way
> around if Apple supplied Envivio with a prerelease DSS before
> it became
> publically available).
> Does an MPEG-4 file need to be hinted to be streamed or does
> DSS include
> real-time packetizers for the MPEG-4 data formats?

An MP4 file definitely needs to be hinted to be streamed: the DSS uses the
hint tracks to figure out how to slice up the movie data in RTP packets. The
hinting process is not done by the server because it is time consuming,
needs to be done only once, and is codec-dependant (or at least, can be).

> And now for the big question:
> Where are the affordable MPEG-4 content creation tools?
>
> Per Bergland
> Carmenta AB - www.carmenta.se
> _______________________________________________
> quicktime-api mailing list
> email@hidden
> http://www.lists.apple.com/mailman/listinfo/quicktime-api


-- Guy Moreillon
-- Team Manager & New Solutions Architect
-- New Solutions, NagraVision, Switzerland
-- Tel: +41 21 732 04 47




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