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[linux-dvb] Re: video4linux converging with linux dvb
Gerd Knorr wrote:
Rob.McConnell@Zarlink.Com writes:
Now I have only recently taken a peek at the V4L2 APIs and understand that
they support video scaling/cropping and some video output capabilities.
However, there are requirements for video encoders (DENC) that don't appear
in the API.
Jep, mainly because there is no driver yet (at least none known to
me). Just pulling some API spec out of thin air without at least one
reference implementation usually doesn't work out that well. Even one
implementation doesn't ensures that you get a reasonable API.
There exist several scaler APIs that have been handcrafted for a
particular STB. Unfortunally the last-generation STBs implemented very
different scaler and analog encoder approaches, it was not really
possible to make a good abstraction. v4l 1+2 mirrors only a tiny
fraction of the possibility these chipsets delivered: video and
stillpicture layers could get stacked in arbitrary orders, alpha blended
or not, colorkeyed or not, in some cases even arithmetic functions
(adding, saturation, ...) between layers were possible. In most cases
these capabilities are coupled with serious limitations (layers were
sometimes tied to particular decoders, sometimes limited to particular
color depths and pixel formats) so that the same code won't work on two
STBs.
In the past the special scaler drivers only implemented the function
subset that was mandatory for a specific application. and provided an
proprietary API that was again wrapped by DirectFB.
Holger
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