Minutes IETF99: netvc
minutes-99-netvc-01

NetVC
IETF 99
Monday 17 July 2017, Afternoon Session II

-------- Agenda --------
* No agenda bashing
* Tim Terriberry will present Daala and Thomas Daede’s slides

-------- Chair Slides --------
Video codec requirements an devaluation methodology: updated Alexey Filippov,
Andrey Norkin, Jose Alvarez

Discussion:
* Mo Zanaty: requirements document is ready for progressing; currently at
version section
        most changes around section 3.1.1
        - no other substantive changes
        - last call at end of may
        - current status: shepherd write-up and passing it on to AD
* Earlier question: whether or not we publish it
        - main impetus is that it’s also be used by other bodies

-------- Test and Evaluation Criteria --------
draft-ietf-netvc-testing
PRESENTER Tim Terriberry (slides by Thomas Daede)

NETVC Testing
* not a lot of changes to testing documents
* have started exercising some of the subjective testing procedures for it
* added a subjective test set (small subset of objective test set)

Statistical analysis
* Generally 12 viewers needed for results to be significant
* SP 50 will be changed in future
* CDEF constrained directional enhancement filter; ended up being significantly
better than CLPF for a number of videos * CLPF: These are all completed; you
can still vote but the results have been calculated * Jonathan Lennox: do we
really intend to have Sintel video only up there twice? * Answer: not sure

Test: https://arewecompressedyet.com/

* Mo Zanaty: for new subjective tests, we will start forwarding to the list if
people are willing to give their feedback on them

-------- Thor Update --------
PRESENTER Steinar Midtskogen

* No updates since IETF 98 (spring 2017)
* Last consensus: have Thor and Daala converge
* Wish list: a tool designed to improve screen content; this has not started yet
* Concerns about buffer retirement: both filters can have vertical filtering
originally fixed by restricting second; quick fix
* Steinar tried to find another fix: combined two passes into one
* Used new subjective test framework AWCY
* Tests were done in AV1, but don’t think would be much difference for Thor
* In all cases objective scores for CDEF are slightly better
* high latency vs low latency results; high latency has more ties
* Objective codec comparisons: did not use objective-2-fast b/c it breaks AV1
sometimes

* AV1 compression history: decreased over the last year, compression gains are
slightly more than 20%, most of that has come in the last three months * AV1
complexity history: y-axis is logarithmic, frames per minute not fps. In order
to get a 20% compression gain, the complexity goes up by about 1000%

* Tim Terriberry:  not sure which commits Steinar measured, but there changes
that allowed you to make much quicker selections; expansion probably made it
much slower, then sped up, faster again * Steinar Midtskogen: Complexity could
go down * Mo Zanaty: data points? Steinar Midtskogen: Twice a month, same
configuration. Selected whatever was in the repository first on the 15th of
each month

-------- Codec Comparison: Thor, VP9, AV1 --------
* Thor and VP9 seemed to have same complexity and compression trade off except
thor can have more compression at the cost of added complexity * AV1 performing
better * If we limit sequence test set to screen content, Thor performs much
better than VP9 but not as well as AV1 * It’s possible to get thor to perform
roughly as well as av1 but with a fraction of the tools and added complexity *
Mo Zanaty: what amount of screen content is in earlier test set? * Steinar
Midtskogen: at least one sequence had a BDR score of 80% better than Thor * Tim
Terriberry:  Wikipedia set (screen capture of someone scrolling through
Wikipedia), a few Twitch videos (Minecraft) * Steinar Midtskogen: with CDEF we
should get a slight improvement * Jonathan Lennox:  you don’t anticipate any
complexity costs? * Steinar Midtskogen: not that huge; for the entropy coder,
some complexity but not a doubling or something like that. Screen content tool
hasn’t been invented yet.

-------- Daala Update --------
PRESENTER Tim Terriberry

* This change is something we discovered while working with the VP9 selections
* How this works for VP9 (VP9 slide)
* Proposal for AV1, but AV1 has all the same problems as VP9 and more problems
on top of that * Mo Zanaty:  comment on resilience these frame numbers that
have been added; you can have a much larger frame number 10 bit 12 bit if you
drop one you actually know that you dropped one * Right. Wanted to have some
consistent way of solving this problem; proposal * Before slide: basically the
situation now. Each one has a buffer of actual pixels in it * After (proposed):
move all the probabilities up into the reference frame; the global motion data
moves up * Whatever is the first frame in your list of reference frame, you
draw reference pixels, and all of your pixels,s probability, all of your motion
data * Mo Zanaty: do you mean to say that before you can update a context after
decoding a non-reference frame, but now you can’t? * TO DO slide: Global
motion; relatively recent, proposal not complete yet, frame size prediction

-------- Chroma From Luma --------
PRESENTER Tim Terriberry; Luc Trudeau, David Michael Barr did most of the work

* Update to CfL proposal
* This presentation topic: Solely used for intra-prediction
* Originally designed Cfl to work within Daala. Hard to do in other codecs
* A lot of Cfl proposals try to build a linear model implicitly from data—this
is not very good * No longer require PVQ (perceptual vector quantization) b/c
we’re doing everything in spatial domain * Decoder nice and simple, just use
parameters that were sent * CfL: encoder side slide, to answer “Are the were
models going to have some constant offset?” * feed into search for best linear
parameters * A couple choices made for efficiency reasons * Mo Zanaty: one
question about your alphas; have you ever looked at to see one plane is useful
for another plane * We code them together, direction on that plane and
magnitude in that direction; probability will increase to the extent that those
are correlated * Boundary handling complicates things b/c (see slide) * 1
pixel, has a small effect on metrics, none visible in picture * Steinar
Midtskogen: does it make sense to use something alpha values to drive
predictions [missed] * Tried in daala, didn’t help.  May be worth revisiting in
AV1;  Answer is maybe.