[M4IF Technotes] questions about mpeg-4 file format

[Richard Shields]

Hi xin chen,
The mdat atom can contain any data in any order you see fit.  There is 
no "framing" data stored in the mdat and thus it has no structure.  It 
is the meta data in the moov atom that gives the data in the mdat atom 
structure but only indirectly.  Typically you would write video or 
audio samples consecutively in decode order into the mdat but there are 
no rules stating that you have too.  You have both audio and video 
tracks it's advantageous to write them in an interleaved fashion.  The 
moov atom will indicate to the player how to locate the samples.
SL Layer... I'll let the more educated among us to answer this one :-)
-Richard
On Thursday, August 29, 2002, at 06:11 AM, xin chen wrote:
> Hi All,
> I read the related part in ISO/IEC 14496-1, and
> quicktime file format, but they are all concentrate on
> the meta-data part, that is the structure of moov
> atom. I want to know more about how the samples are
> stored (in mdat atom, right). Where to get documents?
>
> And about the SL layer, since the SL packet hearder is
> composed according to the SLconfigdescriptor, which is
> stored in ESDescriptor, my question is: the SL packet
> hearder are generated only when the mpeg4 file is
> transmitted, or is it stored already in the .mp4
> (Because on the figure 1 of ISO/IEC 14496-1, the
> terminal get a file from storage medium will need to
> go through deliver layer and sync layer for decoding
> too.)? I think it's a waste to store the same inf.
> twice.
>
> Thank you very much.
>
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