Set-Top-Box Testing, Checking unwanted screen while channel zapping

[RameshMaxEye]

Hi

This is Ramesh from MaxEye Technologies.

I am new to VideoMaster and PQA. Can you please let me know how to detect unwanted screen while changing channels in Set-Top-Box.

Regards,

Ramesh

[Paul-D]

Greetings Ramesh!  Can you better define what you are looking for in your "unwanted screen"?  Are you looking for defects?  A scrambled picture?  No picture at all?  A correct picture, but the wrong channel?  If you can help better define what you are looking, one of our Applications Engineers should be able to follow up and help you get PQA set up. PQA will be the correct solution for this, VMS (formerly VideoMASTER) is more for analyzing static pictures and frames.  Reviewing this article may help you explain better what you are looking for.

Regards,

[RameshMaxEye]

Thanks Paul.

The following are some tests we need to do

1. We need to detect the following during channel change

i. Blank Screen (No Picture)

ii. Distorted or Scramble Picture

iii. Audio distortion

2. Occurance of freezing/distorion when one channel is played continuously

3. Particular string display at random location (finger printing)

4. Audio level testing on the right and left channel

I hope all the above tests can be done with the PQA and AudioMaster.

Regards,

Ramesh

MaxEye Technologies, Bangalore

[nagokul]

HI Ramesh,

In accordance to our previous conversation and owing to the general benefit, I will re iterate the points of our discussion as the reply to this post.

All of these can be achieved with PQA and necessarily need a standard test video which can be programatically generated using NI LabVIEW and VDM. This is required as we cannot afford to have 2 unknown parameters to solve an equation.

1. We need to detect the following during channel change

i. Blank Screen (No Picture)

ii. Distorted or Scramble Picture

iii. Audio distortion

To measure the balnk screen an test video stream which has a alternating squence of two frames with two standard shapes each in a contrasting colour. Noiw the absence of the shapes in the frame is a direct indication of the blank screen and deformity in shape is the distortion of the picture which can simply be measured with PSNR or a basic particle analysis on the image. (User processer required for the second method) 

To measure the audio distortion we need to have a single tone or a standard and known multitone and the FFT on it will give us the amount of distortion on it and the noise floor. Audio mAster provides a very good level of analysis options for that.

2. Occurance of freezing/distorion when one channel is played continuously

A test video with frames having their frame numbers as the only element in the frame is used. Using ocr to read the numbers on them and validate for the increment. The moment there is no increment of numbers and the frame repeats then that particular fram is a filler frame - freezing. (User processor needed)

3. Particular string display at random location (finger printing)

Using OCR and some basic image processing and identification techniques this can be located and read. (User processor needed)

4. Audio level testing on the right and left channel

We can use the Audio SPL option in the NI PQA processors to process and validate it. This also requires a standard monotone to be played as a input signal.

Hope this helps. Do revert for further queries. (You can email me or call me )

Regards,

N A Gokul

[Paul-D]

Ramesh, I contacted our India support and systems team, and understand that you have also begun working with them.  I think it will be best to continue to work with them on the lower level implementation details where you can have more direct contact and work in your own time zone, but I will be glad to help answer some of your questions here, as well.

Before I get to the below explanations, I would like to point out that some of your testing requirements are going to be difficult without a reference stream, or a known video source.  Without being able to control the content, in some cases it is going to be difficult to know what we are looking for.  The quick explanation is that the methods for doing these non-referenced measurements are still being researched by experts in the field.  There are some proposals, algorithms and papers out there on the topic, but as far as we are aware this hasn't been implemented in the real world yet.

Additionally, as I was writing this Gokul added in his comments (Thanks Gokul!), so I will try to build on those with some additional thoughts and details.

As for your tests, here are my initial recommendations:

1. We need to detect the following during channel change

i. Blank Screen (No Picture)

• If HDMI output stops, this will generate a no-signal error from your HDMI analyzer, and the acquisition will stop.  There are a few variations of the errors, but you could capture these, and then act appropriately.
• If the resulting picture is, for example, all black, or all green.
• The Color Processor returns the color(s) found in the frame - PQA Help>>NI PQA Executive and the NI PQA Configuration Panel>>NI PQA Executive Components>>NI PQA Tabs>>Processors Tab>>Video Metric Processor>>Color Processor
• The MSE processor looks for elements that are similar to the defined ROI.  Could look for your black, green, etc area - PQA Help>>NI PQA Executive and the NI PQA Configuration Panel>>NI PQA Executive Components>>NI PQA Tabs>>Processors Tab>>Video Metric Processor>>MSE Processor.

ii. Distorted or Scramble Pictue - This is going to be the tricky one because if we don't have a known video source, a reference, to compare to, its difficult to know when a picture is bad

• Neither of these processors require a reference stream, but they will be difficult to use if you can't control the content on your TV channels as scene changes, and text on the screen will throw them off.
• The Dropped Frames processor looks at the difference between each successive frame.  This can help identify when an error, like a frame being dropped and the screen being completely black occurs.  However, it can also give false results when a scene changes ie: the channel content transitions from a TV show to a commercial.   PQA Help>>NI PQA Executive and the NI PQA Configuration Panel>>NI PQA Executive Components>>NI PQA Tabs>>Processors Tab>>Video Metric Processor>>Dropped Frames.
• The Checkers Processor looks for hard edge transitions, like what be caused by a macroblocking error where a block doesn't update or display properly.  The caveat to this processor is that expected hard edges, like a text overlay in a commercial, will also return high values or false positives.  Additionally, it requres additional processing on the results from the processor to get meaningful data.  PQA Help>>NI PQA Executive and the NI PQA Configuration Panel>>NI PQA Executive Components>>NI PQA Tabs>>Processors Tab>>Video Metric Processor>>Checkers Processors.  Note: I do have a demo that I can share internally to Gokul on how to use the Checkers processor in this way, if we need.
• After these built in functions, as Gokul mentioned you may be able to do some custom processing with the Vision Development Module (VDM) and a custom user processor to go beyond the built-in capabilities of PQA.  I'm not as much of an expert in the vision processing domain, so I'd defer to other supporters on what might be possible.
• Note that due to HDCP limitations, we can not return the raw video data of an encrypted HDMI video stream in the cusom user processor.

iii. Audio distortion:

• If looking for Total Harmonic Distortion, THD or THD+N, PQA has a built-in processor that will deliver these.  PQA Help>>NI PQA Executive and the NI PQA Configuration Panel>>NI PQA Executive Components>>NI PQA Tabs>>Processors Tab>>Audio Metric Processor>>Single Tone Processor.
• If detecting garbled or choppy audio, this is going to be more challenging.
• If the audio is dropping in and out, you may get some meaningful data from the Audio SPL processor which returns level type information, etc.  NI PQA Configuration Panel>>NI PQA Executive Components>>NI PQA Tabs>>Processors Tab>>Audio Metric Processor>>Audio SPL Processor.
• As Gokul pointed out, AudioMASTER may be an option, but it might require some additional analysis, even on the calcuated data. 
  
• Do note that AudioMASTER can not return the raw waveform from an encrypted HDMI audio stream, per HDCP limitations.
• There is also the possibility of using the Custom User processor to analyze the raw audio further.  Again, we can not return the raw waveform of an encrypted HDMI stream per HDCP limitations.

2. Occurance of freezing/distorion when one channel is played continuously

• Dropped frames from above would be a great way to detect if the picture is frozen, because the score between frames would return exactly the same each time because there would be no difference in them.
• Distortion thoughts from above also apply.

3. Particular string display at random location (finger printing)

• This is going to be more difficult due to the random location.  There is an OCR processor, but it needs to be pre-configured with an ROI location.
• As Gokul pointed out, this would likely have to happen via a custom user processor.

4. Audio level testing on the right and left channel

• The Audio SPL Processor from above should meet this requirement.

One other general note.  We are talking about a lot of processing here, and possibly the need for some post processing.  Depending on the power of your PC and the video resolution, it may not be able to perform all of these calculation on-line, or on the fly.  We may also need to look at performing some of this in post processing.

[RameshMaxEye]

Thank Paul and Gokul for the detailed reply.