[Libav-user] Adding alpha channel to h264 encoder

[Andy Shaules]

On Sep 15, 2017 9:49 AM, "Davood Falahati" <falahati.davood at gmail.com>
wrote:

Dear Michael,

Thanks for your reply. I changed the codec to qrtle and I found that there
is an alpha channel added. My problem, however, exists. I translate opencv
Mat with alpha plane to AVFrame. But in the resultin video I don't see the
added alpha plane.

best,

______________________________________________________

Tel: +98 (913) 126-0265 <+98%20913%20126%200265>

On Tue, Sep 12, 2017 at 8:24 PM, Michael IV <explomaster at gmail.com> wrote:

> As far as I know h264 doesn't support alpha.  But  VP8 does.
>
> On Sep 12, 2017 2:06 PM, "Davood Falahati" <falahati.davood at gmail.com>
> wrote:
>
>> Dear community,
>>
>> I have a opevCV Mat frame, call it mask. I decode frames into AVFrame,
>> convert AVFrame to openCV Mat and encode them into AVPacket again.
>>
>> Now, I want to add an alpha channel to my resulting video. Can you help
>> me with that?
>>
>> - FYI, I tried to add alpha channel to openCV Mat and convert it to
>> AVFrame. But it fades whole the video and it mars the color distribution.
>>
>> Best
>> Davood Falahati
>> ______________________________________________________
>>
>>
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>>
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hello. i would recommend writing your own pixel routine to composit the
layers. its a good chance what does work in the libs is developed around a
different use case. formats matter of course so one may want to go through
the highest bits per pix such as 32 for the blend if its detailed and
involves greenscreen types, but fidelity might be a thing and sometimes the
warmth of the transform to rgba and back is undesired.
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