[M4IF Technotes] What is in mpeg-4 system bitstreams?

[AVARO Olivier FTRD/DIH/REN]

> Can anyone tell me what is in the mpeg-4 system
> bitstreams: the SL-packetized streams after the sync
> layer, or the multiplexed streams after delivery
> layer? It seems that it only exists on the certain
> point of the generation and transmission path, not as
> static storage file. If stored as a file, it is
> supposed to be stored as mp4 file format. Is this
> understanding correct?
In MP4, streams are stored in their *natural* form (i.e. transport
independent), therefore not multiplexed and without SL. This is the case
for audio and visual streams as well as for Systems streams (containing
scene description, interactivity, ...).
When you stream them, depending on the transport, you may decide to use
the sync functionality provided by the targeted transport (ex : RTP), or
to use SL (ex : in MPEG-4 streams on MPEG-2 systems) and you may decide
to multiplex them. 
cu,
O.