[M4IF Technotes] Preprocessing for MPEG-4

[the_ether]

You'll be further depressed to learn that MPEG-4 can take a variety of
different input formats. Specifically on the dynamic range, there's a flag
('video_range') that can be set by the encoder to tell the decoder whether
0-255 or 16-235 (240 for chrominance) has been used.
There are six types of RGB-YCbCr conversion supported:
- ITU-R Recommendation BT.709
- Unspecified Video (Image characteristics are unknown)
- FCC
- ITU-R Recommendation BT.470-2 System B, G
- SMPTE 170M
- SMPTE 240M (1987)
The default is 16-235, ITU-R Recommendation BT.709
So, the answer is, it depends on the encoder, MPEG-4 itself, allows for
choice.
graham
----- Original Message -----
From: "Ben Waggoner" <ben   interframemedia.com>
To: <Technotes   lists.m4if.org>
Sent: 16 December 2023 23:53
Subject: [M4IF Technotes] Preprocessing for MPEG-4
> 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
>
>
>
> _______________________________________________
> Technotes mailing list
> Technotes   lists.m4if.org
> http://lists.m4if.org/mailman/listinfo/technotes