In article <3f71da21@news.povray.org> , Warp <war### [at] tagpovrayorg>  wrote:

>   Typically MPEG-4 compresses video to something like 1/4 or 1/8 of the
> size of the equivalent MPEG-1 video (with the same visual quality).

Here is what three of the ISO committee members who developed H.264 (aka
MPEG-4 AVC) reported (get the report on http://bs.hhi.de/~wiegand/JVT.html)
as the "Average bit-rate savings compared with various prior "decoding
schemes", which is about equivalent to the size reduction of the result
video stream, but not taking into account the audio stream:

Codec      MPEG-4 ASP  H.263 HLP  MPEG-2
H.264/AVC  38.62%      48.80%     64.46%
MPEG-4 ASP    -        16.65%     42.95%
H.263 HLP     -           -       30.61%

And this is summarized by them as "Although not discussed in this article,
the bit-rates for TV or HD video (at broadcast and DVD quality) are reduced
by a factor of between 2.25 and 2.5 - when using H.264/AVC coding."

For reference, notice that MEPG-2 at CIF (352*288 pixels) size results in
about the same datarate as an MPEG-1 datastream.  Or in short, MEPG-2 does
not offer much of an advantage over MPEG-1 at the *same* resolution.  This
is not really surprising as the MPEG-2 encoding is a superset of the MEPG-1
encoding.  The main advantage of MPEG-2 is that it specifies much higher
resolutions of up to 1920*1152 at 30 non-interlaced (aka progressive) frames
per second, which then yield a datastream of about 80 MBit/s!

On the other hand, the original intend of MEPG-4 (without AVC) was to
provide a lower-resolution way of transmitting high-quality video data over
low-bandwidth connections.  hence, it is not absolutely correct to say
MEPG-4 is "more developed" than MEPG-2, it is simply better targeted for a
different application domain.

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

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