[FFmpeg-devel] libavcodec/hap : add HapAlphaOnly decoding/encoding

Carl Eugen Hoyos ceffmpeg at gmail.com
Thu Oct 5 10:31:45 EEST 2017

2017-09-29 11:03 GMT+02:00 Martin Vignali <martin.vignali at gmail.com>:
> 2017-09-28 23:24 GMT+02:00 Carl Eugen Hoyos <ceffmpeg at gmail.com>:
>> 2017-09-28 21:50 GMT+02:00 Martin Vignali <martin.vignali at gmail.com>:
>> > After comments about the previous patchs
>> Please explain how this encoder and decoder can be used
>> from the FFmpeg cli: What kind of input could be used, what
>> could be done with the output?
>> I believe you force every user to add an additional filter
>> to do anything useful, please convince me that this is wrong.
>> Hello,
> I didn't design the HAP codec, so my answer mostly follow the comments
> of Tom Butterworth. (in the previous discussion of decoding/encoding)

But this isn't about the HAP codec, but about its representation
within the existing FFmpeg framework.

> Like it seems that the Hap Alpha Only is only design to be use
> for alpha channel encoding

But FFmpeg does not define "only alpha"...

> (not to encode gray), it use in this new patch  : RGBA
> input/output (using only the alpha channel)

... so we have to choose which pix_fmt we can use to emulate
"only alpha". I believe gray is not only the most expected one
but also the one that makes further work easier than RGBA
(that is not "only alpha" either).

> In a more general way, HAP is only useful when use with GPU
> decoding/compositing (specially in very big resolution, with lot
> of video layer)
> (not the case in the ffmpeg).


> IMO, the ffmpeg support is mostly interesting to convert hap
> file to something else or to check what we can encode with
> the ffmpeg hap encoder.

I don't disagree (on the contrary), I believe we should make it
as easy as possible for users to work with it:
Do you believe that it would be easier for users if HAP alpha only
is represented as FFmpeg RGBA or gray?

Thank you, Carl Eugen

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