[FFmpeg-devel] [PATCH] libvpx: Enable vp9 alpha encoding

[Ronald S. Bultje]

Hi Vignesh,

On Thu, Jul 7, 2016 at 2:44 PM, Vignesh Venkatasubramanian <
vigneshv-at-google.com at ffmpeg.org> wrote:

> On Wed, Jul 6, 2016 at 4:50 PM, Vignesh Venkatasubramanian
> <vigneshv at google.com> wrote:
> > On Fri, Jul 1, 2016 at 3:03 PM, Ronald S. Bultje <rsbultje at gmail.com>
> wrote:
> >> Hi,
> >>
> >> On Fri, Jul 1, 2016 at 5:27 PM, Vignesh Venkatasubramanian <
> >> vigneshv-at-google.com at ffmpeg.org> wrote:
> >>
> >>> On Fri, Jul 1, 2016 at 12:48 PM, Ronald S. Bultje <rsbultje at gmail.com>
> >>> wrote:
> >>> > Hi,
> >>> >
> >>> > On Fri, Jul 1, 2016 at 3:29 PM, Ronald S. Bultje <rsbultje at gmail.com
> >
> >>> wrote:
> >>> >
> >>> >> Hi,
> >>> >>
> >>> >> On Fri, Jul 1, 2016 at 3:12 PM, Vignesh Venkatasubramanian <
> >>> >> vigneshv-at-google.com at ffmpeg.org> wrote:
> >>> >>
> >>> >>> On Fri, Jul 1, 2016 at 11:06 AM, James Almer <jamrial at gmail.com>
> >>> wrote:
> >>> >>> > On 7/1/2016 2:53 PM, Ronald S. Bultje wrote:
> >>> >>> >> Hi,
> >>> >>> >>
> >>> >>> >> On Fri, Jul 1, 2016 at 1:40 PM, James Zern <
> >>> >>> jzern-at-google.com at ffmpeg.org>
> >>> >>> >> wrote:
> >>> >>> >>
> >>> >>> >>> On Fri, Jul 1, 2016 at 10:07 AM, Carl Eugen Hoyos <
> >>> cehoyos at ag.or.at>
> >>> >>> >>> wrote:
> >>> >>> >>>>> Do we have decoder support (for either vp8 or vp9) for these
> >>> files?
> >>> >>> >>>>
> >>> >>> >>>> No, only encoding and muxing.
> >>> >>> >>>
> >>> >>> >>> Seems like a feature request, but no reason to block this one
> if
> >>> the
> >>> >>> >>> vp8 one is here.
> >>> >>> >>
> >>> >>> >>
> >>> >>> >> I'm not sure I have an opinion on this... But it feels strange
> to
> >>> allow
> >>> >>> >> encoding of content we cannot decode. Being ffmpeg, how do we
> >>> recommend
> >>> >>> >> people handle the files created with this feature, if not by
> using
> >>> >>> ffmpeg
> >>> >>> >> itself?
> >>> >>>
> >>> >>> One plausible reason is that Chrome can decode this. So it will be
> >>> >>> useful for people who already have ffmpeg in their pipelines and
> want
> >>> >>> to create such files. And like James Almer mentioned, this isn't a
> >>> >>> first. VP8 Alpha has been this way too.
> >>> >>
> >>> >>
> >>> >> The fact that something is the way it is, does not prove that it is
> >>> >> therefore right, or that we should therefore continue doing it that
> way
> >>> in
> >>> >> other cases.
> >>> >>
> >>> >> So you're suggesting that it is perfectly fine for people to use
> Chrome
> >>> as
> >>> >> decoder if FFmpeg is the encoder. What if people don't have Chrome
> >>> >> installed? Or what if they want a way of UI-less batch-processing
> such
> >>> >> files, e.g. what if a service like Youtube/Vimeo wants to allow
> upload
> >>> of
> >>> >> vp8a/vp9a files without invoking Chrome for decoding?
> >>> >>
> >>> >
> >>> > Additional evidence in [1], [2].
> >>> >
> >>> > There absolutely seems to be interest in support for vp8a/vp9a
> decoding
> >>> > outside Chrome. I'm not saying you should implement it in all
> multimedia
> >>> > frameworks ever created in human history, but doing it in one of them
> >>> (e.g.
> >>> > ffmpeg, since it already supports encoding) certainly sounds helpful?
> >>> >
> >>>
> >>> I'm not saying alpha decoder shouldn't ever be implemented in ffmpeg.
> >>> I'm just saying that it shouldn't be a reason to block this patch. :)
> >>> Sorry if i wasn't clear before.
> >>
> >>
> >> I totally understand that you would think that, since it means you don't
> >> have to do anything :).
> >>
> >> But there's an issue with this thinking. We're essentially already the
> >> dumping ground for anything multimedia-related nowadays. After all, we
> >> maintain it and keep it working (assuming basic tests), things couldn't
> get
> >> much easier than that, right? But is it actually useful to anyone? I
> mean
> >> not just useful for you, but useful to a wider set of people, at least
> in
> >> theory.
> >>
> >> If there's no decoder, I would claim that the wider utility of this
> thing
> >> is essentially zero. And that's somewhat of a concern.
> >>
> >> So, how do we get a decoder? vp8a suggests that just waiting for one to
> >> spontaneously combust out of thin air just doesn't work. So I'm
> suggesting
> >> you provide us with one. It's ok if it uses libvpx instead of ffvp8/9.
> >> Since vp8a encoding is already in, I won't ask for a vp8a decoder
> either.
> >> I'm just asking for a vp9a decoder. It might even be OK if it's
> implemented
> >> on top of ffmpeg instead of inside libavcodec (I'm not sure how others
> feel
> >> about this), i.e. just something that invokes libavformat to parse a
> webm
> >> file, create two decoders to get the yuv and a planes, and then merge
> them
> >> together into a yuva420p picture. I'm just asking for something _small_
> and
> >> _simple_ (i.e. not "Chrome") that we can point users to when they ask
> "how
> >> do I decode vp9a files".
> >>
> >> I asked on IRC (#ffmpeg-devel) and several people concurred:
> >>
> >> <BBB> jamrial: so … I’m looking for a second opinion here, like, an
> >> independent one… am I being too hard on these guys for saying “an
> encoder
> >> needs a decoder”?
> >> <JEEB> BBB: I do tend to agree that in general it goes dec->enc, or
> both at
> >> the same time. be it a fully lavc decoder or just utilizing a decoder
> >> library
> >> <jamrial> BBB: no, you're not being hard
> >>
> >> So it seems I'm not entirely alone in this opinion within the ffmpeg
> >> developer community.
> >>
> >
> > Alright, i have a working patch for the decoder locally (i will push
> > that to the ML shortly).
>
> Here it is: http://ffmpeg.org/pipermail/ffmpeg-devel/2016-July/196403.html


Thanks, that resolves my concerns.

Ronald