[Mp4-tech] Constant Bit Rate mp4

[Andy Beer]

Hi All,
It seems that there are ways to get H264 (AVC) video encoded at near
constant bit rate.
The Main concept H264 encoder has a CBR mode and allows the user to
modify the VBV setting (including buffer occupancy)
Entering a value of 130,202 (haven't figured out what units these are)
constrains the rate to the point that the target hardware (described
originally) can play the file properly. Charles asked about exceeding
the recommended buffer size.....As far as I can see the software players
(eg Media Player, VLC player, Winamp etc) can accommodate the excess.
But these players have access to the data on disc so the buffering
requirement is different.
The target application for my files requires the CBR data to be
multiplexed in a MPEG-2 Transport Stream. This stream must be "real CBR"
and the rate will be fixed at the highest rate excursion of the AVC
encoder. You might ask whether an H264 encoder should provide any great
improvement over an MPEG-2 encoder when forced to work at CBR. The big
improvement would come from throttling down the rate whenever the new
coding tools can better exploit any image redundancy. A big buffer could
exploit some of the dividend even if it were filled at a fixed rate. At
CBR with a small buffer you can't put any cash in the bank for a big
spending spree during rapid scene changes. Then when the scene fades to
black all you can do is pad out the data. It does seem to look quite a
bit better in practice so there is some hope!
AB 
Andy,
I can't answer your questions, but please deinterlace the content
appropriately also. :)  When I was on a KLM plane yesterday most of the
content on the VOD system showed pretty bad interlacing artifacts.
regards,
--Marco
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org]On Behalf Of Andy Beer
Sent: Wednesday, January 03, 2024 1:40 PM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] Constant Bit Rate mp4
Andy,
> 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))

That's the recommended size, but do you know whether exceeding that
actually presents a problem?  (In other words, does this present an
actual problem in
testing?)
-- Charles
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
Andrew Beer
Inflight Studios
Tel:    020 7400 0700
Direct:020 7400 0794
IFP Mobile: 07876 552504
andy.beer inflightproductions.com