VIP handling of Interlaced video

I am struggling with the processing of interlaced NTSC video using the VIP 9.0 cores, and hope someone here can give me some advice.

My project needs to take two NTSC interlaced inputs from ADV7180 decoders, do some processing, and then send the output to a single ADV7171 encoder. I am using an alpha mixer on the output stage of my chain of VIP components, and while I can send a test pattern such as color bars (generated with the VIP test pattern component) through the alpha mixer, none of my interlaced source video comes through.

The test pattern is setup to generate interlaced 4:4:4 output, and I am sending the NTSC data to the mixer in that format too. I am starting to suspect issues with interlaced video in general with the mixer. Maybe someone can shed some light on it for me.

I have another project that works fine doign the same thing, with the difference being that I deinterlace the NTSC input video, and output to a progressive display. That works. In this case I need to output interlaced video though, and as there is no VIP "Interlacer" component, it seems that I have to keep the data in interlaced form throughout my VIP flow.

The current VIP chain looks something like this:

For both NTSC inputs:

CVI (8-bit)->CPR (16-bit)->Clipper (to 243 lines)->CRS (to 4:4:4)->Frame Buffer

Each of the two frame buffers, along with a test pattern generator, connect to an Alpha Blending Mixer component. The test pattern generator is set to produce color bars, interlaced, in 4:4:4 format.

The chain from the Alpha Blending Mixer to the output looks like this:

Mixer->CRS (back to 4:2:2)->Frame Buffer->CPR (8-bit)->CVO

The only thing I can get to come through is the background layer - the color bars.

Any advice is appreciated!

Jim

15 Replies

Altera_Forum
Honored Contributor
16 years ago
Yeah I'd be suspect of how the mixer is going to handle it. The video IP user guide indicates that the mixer will accept interlaced data but with the following disclaimer:

--- Quote Start ---
Interlaced/Progressive: Progressive. Interlaced data is accepted but the offset from the top edge for each foreground layer has to be adapted in consequence.
--- Quote End ---

Here is what I would do in order of increasing time commitment.
1 - double-check that you are correctly enabling the individual foreground channels (I assume you are using a NIOS for this).
2 - I would try a test pattern other than colorbars for the background. Something with some horizontal content.
3 - simplify the design so that you only have one video input for the sake of test. Stay with this until you get it working.
4 - Signaltap the inputs to the mixer.
5 - Simulate the design.

Jake
Altera_Forum
Honored Contributor
16 years ago
Jakob,

Thanks for the quick reply, and I am already somewhat down that path.

I don't have a NIOS in the design at the moment, although it is planned. Right now I am using a JTAG master to run TCL scripts to write to the control registers on the mixer.

When processing interlaced video, am I correct in thinking that all the processing is done on a FIELD basis (F0 or F1) rather than a frame basis, unless I deinterlace the video?

Do you know of any way to produce interlaced video using the VIP tools, once it is in progressive format in a frame buffer?

Thanks!

Jim
Altera_Forum
Honored Contributor
16 years ago
Yes you are correct in assuming that every field would be processed as if it were a frame. However, I've never run interlaced data through the mixer and don't know the behavior.

I believe Altera has a simple interlacer block which I think is due to be released with 9.1. However, if you ping the right guys maybe they can give you a pre-release version. I've written my own simple interlacer but all it does is drop every other line. I'm sure you could write something similar. If you do so, you'll have to process everything in progressive format and interlace at the end. I haven't had the need to write a true interlacer (with the frame buffer) yet but I will shortly.

Since you are using a JTAG master, I'd double-check to make sure those registers are getting set right. If it were me I'd throw in a NIOS really quick and some on-chip memory.

Jake
Altera_Forum
Honored Contributor
16 years ago
Any idea who I contact at Altera? ;-) I would be happy to beta test a new Interlacer core! ;-) I've got an immediate need for it, and am under maintenance on all my software at the moment - just paid for it about 2 months ago.

Thanks.

Jim

P.S. I just contacted the local FAE I deal with, and he is going to rattle the tree at Altera and see what he can find out for me....
Altera_Forum
Honored Contributor
16 years ago
Hi,

Your FAE should be asking for the reference design called V2. This reference design contains a beta version of the interlacer although this is not a full interlacer and it just drops every other line.

When processing interlaced video, the mixer, like many VIP cores, will do the processing on a field basis. In order to do the mixing, you probably will have to ensure that F0s are properly synchronized together because the mixer will just use whatever is coming in. The disclaimer note on the VIP guide means that when specifying (x,y) coordinates for the top-left pixels you have to divide y by 2.

The double buffer supports interlaced video but the triple buffer does not. If you turn on the drop or repeat checkboxes you may end up with a stream that contains successive F0s or successive F1s.

vgs
Altera_Forum
Honored Contributor
16 years ago
VGS,

Thanks, and your explanation of how the VIP handles interlaced video explains a lot. I've been selecting triple buffers, and have issues if I send more than one video source into the frame buffer. I'll try to process with double buffers and see if it makes a difference.

My last test on Friday involved going back to progressive video by using 2 deinterlacers, and that works, but of course the output is all over the place vertically on my monitor, which is expecting interlaced NTSC, not progressive.

I'll be talking to the FAE this morning about access to that core. Thanks again.

Jim
Altera_Forum
Honored Contributor
16 years ago
jfmorris, I'm very interested by the interlacer core too!
Please let me know, by updating this post, if your FAE is able to give you the beta version of the interlacer core!
Thanks
Altera_Forum
Honored Contributor
16 years ago
The Altera DSP specialist will be in my office later today. He's the one who acts as the front-end for the VIP. I'll ask him about it.

Jake
Altera_Forum
Honored Contributor
16 years ago
I have the V2 reference design, which includes new Beta versions of the following cores:

Clocked Video In
Clocked Video Out
Frame Buffer
Deinterlacer
Interlacer

All of them have various modifications to properly handle interlaced video. Unfortuntely, with Quartus 9.0 sp1, I cannot compile either the reference V2 design, or my own design. I bomb out with the following error (twice) when the VFB (Frame Buffer) is being elaborated:

Error: IP Generator Error: Variable msg_field_interlace_4 does not exist in the variable life table

At that point Quartus II gives up and we are done.

Unfortunately I don't think the regular frame buffer will work, as the beta one has a new checkbox for enabling "Interlaced video compatibility".

Jim
Altera_Forum
Honored Contributor
16 years ago
Did the reference design include some accompanying patches for the VIP cores? My understanding was that it would.

Jake

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VIP handling of Interlaced video

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