[Mp4-tech] DMIF, Flexmux, ISMA and RFCs

[Nick Ryan]

Hi there,
I am trying to clarify my understanding of how the DMIF, Flexmux, the
ISMA standard, RFC3016 and RFC3640 are related.
Here are my questions:
- How do the ISMA standard and RFC 3640 relate to each other in terms of
future standardised IP streaming of MPEG4?
- What servers and clients currently use RFC 3640 for streaming
delivery? Are there any that are planning support?
- As RFC 3640 specifies delivering Access Units and Flexmux specifies
multiplexing SL packets are these two basically mutually exclusive?
- If this is correct is there a standard way of streaming Flexmux
streams over RTP?
- With respect to RFC3640 is there any standardised way to transcode or
map information from the SL to fields defined in the RTP payload format?
- Does anyone have an opinion on the relative merits of using a single
Flexmuxed stream or separate elementary streams for IP streamed content
delivery with respect to packet header overhead and multiplexing
complexity if we are looking at content delivery that will dynamically
change based on user interaction?
I have read the MPEG4 standard and RFCs. I do not have the ISMA standard
but have read discussions about it.
This is what I understand so far and please correct me if I am wrong:
- Flexmux provides a means of multiplexing SL packetized streams.
Flexmux would be implemented within the DMIF layer below the DAI.
- RFC 3640 defines transport of audio,video and application MPEG4
elementary streams. RFC 3640 implementations can be built to
interoperate with RFC 3016 video payloads.
- RFC 3640 defines the transport of MPEG4 Access Units. The information
that SL packet headers contain are translated to RTP packet header
information.
- An implementation of a compliant RFC 3640 receiver within the DMIF
layer would extract the RTP header data and encapsulate the AUs inside
SL packets with the appropriate information. These would then be
presented to the application via the DAI.
- Generally, the ISMA standard defines amongst other things using
RFC3016 for video delivery.
Thanks!
Nick Ryan
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