Subject: [video-codec] Bitrate ranges for requirements and testing drafts

From: Thomas Daede <[email-masked]>
Date: Mon, 21 Sep 2015 14:36:59 -0700

I currently have this for the BD-Rate ranges in my Testing draft:

    Low bitrate: 0.005 - 0.017 bpp
    Medium bitrate: 0.017 - 0.058 bpp
    High bitrate: 0.058 - 0.2 bpp

where bpp is width * height * framerate. These rates are spaced equally
on a logarithmic scale.

bpp is not perfectly resolution independent. We could instead specify
targets based on video resolution instead.

Another way to specify the ranges is by metric score, rather than rate,
but determining the ranges is a bit problematic. How I would probably
set these ranges would be to take these rates, and use them to set the
bounds based on a well regarded encoder (x264, for example).

The Requirements draft also currently specifies overlapping ranges. I
don't really see any reason to overlap them.

Rate targets are also needed for comparing videos. I suggest the
logarithmic centers of these rates:

Low: 0.009 (450kbps 1080p24)
Medium: 0.03 (1.5Mbps 1080p24)
High: 0.1 (5Mbps 1080p24)

Let me know how these currently fit into the use cases.

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From: "Timothy B. Terriberry" <[email-masked]>
Date: Wed, 23 Sep 2015 14:06:35 -0700

> bounds based on a well regarded encoder (x264, for example).

This is also highly content-dependent (i.e., it can vary by an order of 
magnitude). So if you want to go this way, you will likely have a 
different range for each set of test sequences, which may not be a bad 
thing.

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From: Harald Alvestrand <[email-masked]>
Date: Thu, 24 Sep 2015 10:07:28 +0200

On 09/23/2015 11:06 PM, Timothy B. Terriberry wrote:
> This is also highly content-dependent (i.e., it can vary by an order
> of magnitude). So if you want to go this way, you will likely have a

Uh...... perhaps we should bite the bullet and just set rate control
parameters?

>
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> video-codec mailing list
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From: Thomas Daede <[email-masked]>
Date: Thu, 24 Sep 2015 12:12:03 -0700

> Uh...... perhaps we should bite the bullet and just set rate control

I'm not sure what you mean here - you mean specify quantizers as the bounds?

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From: Harald Alvestrand <[email-masked]>
Date: Fri, 25 Sep 2015 16:29:32 +0200

> I'm not sure what you mean here - you mean specify quantizers as the bounds?

I've argued for a long time that a codec that can't be rate-controlled
is useless for interactive Internet usage - and that therefore, it makes
sense to actually use rate controls when we test the codec.

We're now faced with a situation where we have specified test conditions
that specify certain bitrate targets - but the only means we have of
hitting those bitrate targets is to encode the file over and over again
until we find something that has a bitrate that matches our target.

If we could, instead, specify the bitrate target when encoding the file,
and measure the resulting quality metrics on the file after bitrate
controls are applied, we would have, in my opinion, a test scenario that
more resembles real-life usage.

Of course, fixed-quantizer encodings are reasonable to use when trying
to measure the impact of codec tweaks that don't interact with the rate
controls.
But that's not the only thing we want to measure.