[linux-dvb] video4linux converging with linux dvb

[Rob.McConnell@Zarlink.Com]

Hi Folks,

I sent out a mail yesterday to the linux-dvb ML questioning the
capabilities of the Linux DVB V4 API for supporting STB/iDTVs.  The current
V4 API supports the frontend, demux and audio/video decoders quite well
(even for STBs), but still lacks proper support for video scaling, video
encoder (DENC) and other capabilities such as PiP.

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.  For example, there isn't the ability to specify RGB, YUV, YC
(S-VHS), CVBS output configurations, enabling/disabling Macrovision,
enabling certain test modes (e.g. colour bars), CGMS support, etc.  These
are typical functions that DENCs provide as well as WSS, VPS, close
captions and teletext insertion all in the VBI.   Now the Linux DVB V4 API
has touched on the WSS, VPS and teletext issues, but I would have thought
it better to have all this capability "packaged" together.

Then there's the issue of video scaling.  The current Linux DVB V4 video
API  I modified to allow the presentation format to set internal
scaling/centre cut-out/letterbox modes that are usually integral to the
MPEG video decoder hardware.  In the UK the end aspect ratio is dependent
on the broadcast aspect ratio as well as transmitted AFDs (active format
descriptors), but the user (or application) can override this to display a
1/4 or 1/16 or other-size video _underneath_ the graphics/OSD plane.  So,
then there's the question of whether the Linux DVB V4 video API should be
extended to handle scaling (especially for STB chips) or to use the
V4L/V4L2 API.  It seems very disjoint to have 2 separate APIs, when the
underlying hardware is closely coupled.

So the next logical question is should both camps start to think about
collaborating together to form a single set of APIs that handle both
analog/digital cards as well as STBs?  AFAIK, the Linux DVB API was a
branch off from the V4L work a few years ago.  With both camps now looking
at supporting digital cards/STBs then it would make sense to remove
duplication of code and time.

Any thoughts/comments?

Rob : )