[FFmpeg-devel] [PATCH 2/4] lavfi/opencl: Handle overlay input formats correctly.
gyandoshi at gmail.com
Wed Nov 14 08:26:55 EET 2018
On Wed, Nov 14, 2018 at 7:00 AM Song, Ruiling <ruiling.song at intel.com>
> > -----Original Message-----
> > From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf Of
> > Mark Thompson
> > Sent: Sunday, November 11, 2018 9:55 PM
> > To: ffmpeg-devel at ffmpeg.org
> > Subject: Re: [FFmpeg-devel] [PATCH 2/4] lavfi/opencl: Handle overlay
> > formats correctly.
> > On 29/10/18 05:56, Ruiling Song wrote:
> > > The main input may have alpha channel, we just ignore it.
> > This doesn't ignore it - it leaves it uninitialised in the output, so a
> YUVA or GBRAP
> > output will never write to the A plane. I don't think that's what
> you're intending.
> What I wanted to say is ignoring main input alpha channel.
> The question is what the user would expect the result alpha channel
> I don't have a clear answer to it, so I just keep it uninitialized.
The s/w overlay filter does this to produce the output alpha:
main_alpha += (1-main_alpha) * overlay_alpha
Better to keep it consistent, IMHO.
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