Using PXI-5431and PXI-1411 to test MPEG-2 encoder/decoder

[Havarti]

I am looking into a way to test an MPEG-2 encoder/decoder.  I have found the PXI-5431, that can generate a NTSC signal which is what I need and the PXI-1411.  So, I guess my question is: would this be a good set up to use the 5431 to generate a signal and the 1411 to acquire the signal and do some comparisons to the two.  Has anyone done this type of testing?  What type of comparisons could be done to the two video signals to verify signal quality(I know very little about video signals)? Or maybe acquire using the PXI-5122?

Thanks,
Brian

[chericks1]

Hi Brian,

There are no issues in terms of the NI 5431 generating NTSC video signals.  However, it generates very specific waveforms at specific sample rates.  Were you planning on using a MPEG decoder to create those waveforms?  The NI 1411 is good at looking at the image, but in terms of looking at the quality of the image, MicroLEX Video Master and a NI 5122 would be great.

Please provide some more details on how you want to test the MPEG encoder/decoder, and what that system provides.

Best regards,

Chad Erickson
Applications Engineer

[Havarti]

Chad,

The card can be configured to decode and encoded MPEG video.  I want to test is by using two card, one to encode the other to decode.   I will generate into the encoder the decoder will then decode the stream and then use either the 1411 or 5122 to acquire the signal.   I would then do some measurements acquired signal.  I would like to make such measurements as Frequency Response, Video Resolution, SNR, and composite signal amplitude measurements.

How are measurements done with these two cards?  What software is need IMAQ, NI-Vision, other?  It seems people are making pretty sophisticated video measurements with the 1411. Isn't this just a video capture card.  How is this being done?

Thanks for your time,
Brian

Message Edited by BrianPack on 08-24-2005 10:38 AM

[chericks1]

Hi BrianPack,

I have some questions.  Please be much more detailed and specific in your next response.  Try not to use pronouns.  Instead, every time you want to use the word "it" or "card", instead use the proper names, such as the "PXI-5122".

What card are you referring to in your first sentence?
When you say (it) "can be configured to decode and encoded MPEG video", do you mean to say you are attempting to encode analog video?
With all the MPEG encoding and decoding, which cards are you referring to?  Your two cards, or two NI modules?
When you generate into the encoder, are you wanting to generate from the NI 5431?  If this is true, what video standard are you wanting to use?
The Frequency Response, Video Resolution, SNR, and composite signal amplitude measurements should be available with the NI 5122 and MicroLEX VideoMaster.  I'm not sure about the NI 1411 because I only support NI's Modular Instruments, but here are the specification sheets for VideoMaster:
http://www.microlex.dk/products/video/videomaster-component.pdf 

If you want more information on the NI 1411, it would be best to post a message on the IMAQ/Vision forum.  For now, please respond with more specific information and I'll be happy to assist you!

Chad Erickson
Applications Engineer

[Havarti]

Chad,

I want to connect two UUTs (Unit Under Test) together, one to encode the other to decode.  I want to use the PXI-5431 to generate composite NTSC into the encoder then acquire the same type of signal off the decoder with either the PXI-1411 or PXI-5122.  So the signal flow would be an analong NTSC signal into the encoder to be MPEG encoded then straight into the decoder to be MPEG decoded and then sent to the either the 1411 or 5122.

Brian

[chericks1]

Hi Brian,

Thanks for the clarification!

You could use the 5431 to generate the video going into your encoder device and the 1411 or maybe the 5122 to acquire the video coming out of your decoder device.  The 5122 and VideoMASTER will show the actual shape of the waveform and you could get the line period, sync and color burst characteristics, and other measurements like that, but not an actual image.  The 1411 will return the actual image, which you could then compare to the original generated by the 5431 using image processing tool in the Vision Development Module, but you won't get the detailed measurements of the waveform.

It really depends on what you want to do, but if the goal is to test the quality of the mpeg encoding and decoding, then comparing the image in to image out seems like the way to go, and thus the 1411 may be the hardware of choice.

Let me know if you have further questions or if this does not resolve your issue!

Chad Erickson
Applications Engineer

[Havarti]

Chad,

Thanks for the responses.  You said if I used the PXI-1411 I could compare the video acquired by the 1411 with that generated by the 5431.  How would this be done?  Would I need the NI-Vision software or some other software package to be able to quantify the video quality?

Thanks,

Brian 

[Havarti]

I just noticed that you recommended the Vision Development module to compare the to signals so please disregard the last message about what software.   How does the vision development compare the to signals?

Brian

[RManion]

Hey Brian,

Are you planning on using the Video Generation Wizard?  If so, this will allow you to create a signal based upon an image input.  The signal will be sent through your hardware, and you can use the 1411 to read the image back in.  After the image is acquired, you could use image processing functions to do a pixel to pixel comparison of the source image to the image read by the 1411.  This process creates a difference image, which is basically the difference in intensity between any particular pixel and its corresponding source pixel.  This is a good representation for several kinds of error.  This is just one example of a measurement you could make from the image.

On the other hand, if you are sending an arbitrary signal to your hardware, it would be best to read the result on something other than the 1411(ex: 5122).  Long story short, the 5122 is a digitizer that will allow you to view the signal coming in, whereas the 1411 is a framegrabber that will interpret the signal and create an image.  Which board you go with should ultimately be determined by what type of tests you are performing.

Hope this helps!

Robert