Re: Video overlay generator

On 15 aug, 14:34, Frank Raffaeli <SNIPrf_man_frT...@xxxxxxxxx> wrote:
On Aug 15, 2:14 am, Andreas <bloodd...@xxxxxxxxx> wrote:



On 13 Aug, 15:32, bloodd...@xxxxxxxxx wrote:

Hi!

Im starting a design process for a utility that needs to implement avideooverlaygenerator. Previously we've been using the "classic"
STV5730-chip for text-overlaybut since this IC is quite outdated and
hard to get hands on we've decided to implement our ownoverlay
generator.
The reason for this is that we want to be able to display graphical
items(such as a customer logo) and also because we need delecate
control of synchronization signals.
Thevideosignal is CVBS in/out and could be either PAL or NTSC.
We've thought of using these three major parts to implement the
design: avideodecoder (f.e. Texas Instruments TVP5150) that feeds a
digitalvideostream into a FPGA (f.e. Xilinx's Spartan 3), that
performs blending between the digitalvideostream and a "overlay
buffer" that gets generated from a microcontroller, and finally into avideoencoder (f.e. Analog Devices ADV7171).

I would really appreciate some feedback or input to this solution if
someone out there has done something similar.

Should I count with a noticeablevideoquality loss due to the AD ->
DA conversion?

Our application has some specific requirements, f.e. there is a frame
counter that has to be updated each frame which probably will require
us to implement a character generator inside the FPGA.

Do you think this is a viable solution - is there any existing ICs
that will do some or most of this work for me?

Best regards,
Andreas Eriksson

No suggestions?

Best regards,
Andreas Eriksson

Most of the loss will be in the chroma-luma separation. If you can
somehow overlay a simple color graphic by replacing the video with the
overlay (like an OSD), then you can pass-through the CVBS and only
change the signal where the overlay is.

The reason video / audio decoders are going out of style is because
now they're all custom ASICs. Even for analog signals.

Frank

Yes, this is very possible, I have done it with some simple analog
switches (HC4053).
In case of color, you also need to insert the right chroma phase, that
means in PAL
that you need to phase lock a 4.43 MHz xtal and get the H/2 info too,
apart
from the H PLL and V sync.
And, depending on how you create the chroma phase, also 2 90 degrees
shifted apart
modulators.
It is all low power analog stuff, could easily fit on one board, if
the graphics is fixed
(for example a logo) you could clock from an EPROM (via a PLL locked
clock to H), or else use SRAM and provide some processor on with an
interface
to update the SRAM.
The digital crude way would be to digitize, add you graphics, and make
analog
again, using a high end PC for enough speed to do it in real time.
Both methods likely require some programming knowledge too.
What method depends on quality required and power available, knowledge
of video
basics.... time, money.... what not.




.

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