[Mp4-tech] Constant Bit Rate mp4

[Andy Beer]

Experts,
I have been evaluating the following mpeg-4 video codecs:
Sorrenson
Main Concept
Envivio
Nero
The video I need to encode is Advanced Simple Profile @ Level 5.
It has some particular conformance constraints as it must play out on
Panasonic Inflight Entertainment systems.
The target system is somewhat hybrid in as much as the player unit now
contains mpeg-4 decoders, the server and distribution system are,
however, legacy designs. The latter require the bit stream to be
constant bit rate and multiplexed in an MPEG-2 Transport Stream. 
I can't find an MPEG-4 ASP encoder that outputs true CBR although all
the above can be configured to produce it.
Over several seconds of material the rate averages to the required bit
rate but particular seconds may be triple the required rate.
When I use professional analyzing tools to monitor buffer usage, all the
encoders I have used exceed the recommended VBV buffer size for Advanced
Simple @ Level 5 (1,835,008 bits (ie 112x16384))
I tried the Mindego Analyzer and the Interra Vega.
For a fixed bit rate of 2,500,000 bits per second, my codecs require the
following size VBV buffers:
Main Concept: 8,033,600 bits
Envivio	  2,178,560 bits
Sorrenson	  7,058,560 bits
Nero		  3,390,000 bits
Should I be surprised to find this? I appreciate that MPEG-4 video
codecs are sufficiently good at detecting redundancy that they lend
themselves to VBR. Is there a CBR solution?
Andrew Beer
Inflight Studios
Tel:    020 7400 0700
Direct:020 7400 0794
IFP Mobile: 07876 552504
andy.beer inflightproductions.com