[M4IF Technotes] Preprocessing for MPEG-4

[Ben Waggoner]

Hello all,
    I've been working on testing some MPEG-4 encoders, and it's been a
difficult slog, since they all support different input formats, and often
seem to be doing different kinds of color space conversions even on the same
source.  I long for the idea world where every encoder can use the native
libraries for QuickTime and DirectShow, and can take native YUV codecs as
source without any color space conversions.
    Anyway, I was wondering what kind of preprocessing MPEG-4 is optimized
for.  Most video sources will use the 601 luma range of 16-235.  Most (but
not all) web delivery codecs expect a luma range of 0-255, where a 0 will
match RGB black elements on the same screen.  How about MPEG-4?  Should my
black be Y=0 or Y=16?
    Also, I've heard that MPEG-4 has some ability to automatically
compensate for different properties of the playback display, like doing
different gamma compensation for Mac and PC.  If this is so, could anyone
offer a brief summary of how this works?  Is this source tagged with what
the original gamma was, so it can be corrected on playback?
Ben Waggoner
Interframe Media <http://www.interframemedia.com>
Digital Video Compression Consulting, Training, and Encoding