[Mp4-tech] Question about QuickTime Pro

[Dave Singer]

At 4:57 PM -0400 8/19/04, Ryan Lei wrote:
>Sorry for the mass email. I have this question for the QuickTime expert.
>
>I am using QuickTime Pro to create 3gp files with H.263 elementary 
>streams in it. When I do transcoding
>I can specify the frame rate and I frames interval. After I create 
>the 3gp file and open it in the analyzer, I can
>See there is a SyncSampleBox, which tells me which frames are I 
>frame. However, when I extract the H.263
>Elementary stream out from the 3gp file, and open the elementary 
>stream in the analyzer, it tells me only
>The first frame is the I frame, all other frames are all P frames. 
>If I open the stream in a Hex Editor and check
>the frame start code of H.263 stream, it actually shows that there 
>is only 1 I frame. Can somebody tell me what's
>going on.

Well, this isn't really an MPEG-4 question at all, since it's a QT 
and H.263 question.
The frames you are looking at are independently decodable (i.e. they 
do not use prediction), and are thus valid 'sync' points in the 
stream.  For various reasons, they are coded using P-frame syntax. 
Hope this helps.
>
>Ryan Lei
>ATI Technologies Inc.
>Handheld Products Team
>33 Commerce Valley Dr. East
>1-905-8822600 ext 2712 (o)
><>www.discover.uottawa.ca/~leizj/
>
>
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-- 
David Singer
Apple Computer/QuickTime
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