Video stream errors

Help and support for the BATC DTX1 ATV digital encoder and modulator system
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vk2crj
Posts: 6
Joined: Thu Oct 29, 2015 8:23 am

Video stream errors

Post by vk2crj » Fri Oct 30, 2015 6:59 am

I just recently bought a DTX1and found that two different receivers were loosing video data at the same time. This showed as dropped or corrupted frames and one of my RX's reported video stream errors. I ran a test with a direct (attenuated) connection from TX to RX to eliminate any external interference with the same result.

Eventually, I was able to trace the problem to unreliable WSS format selection. My camcorder outputs 16:9 with WSS and the DTX1 input aspect ratio was set to auto. I found if I manually switched between 16:9 and 4:3, I could generate the same loss of video data. So I've set the aspect ratio to 16:9 and the problem has gone away. It would seem on AUTO, the aspect ratio is occasionally changing state. The WSS signal looks good on the scope.

I hope this helps anyone who may have experienced the same problem.

M0LDZ
Posts: 73
Joined: Sat Apr 04, 2015 12:59 pm

Re: Video stream errors

Post by M0LDZ » Sat Oct 31, 2015 12:56 pm

Strange. The WSS signal is detected in the video ADC chip, and appears in a register therein. We have one routine which reads the bit every 100ms and sets a flag if true - if the bit is not set for 5 consecutive reads, the flag is reset to indicate 4:3 instead. Another process reads this flag every second and if it has changed stops the encoder, reconfigures it, and re-starts it. Such an activity would inevitable give rise to video stream errors since the feed halts momentarily. So I have a few questions:

1. Is your video feed PAL or NTSC
2. Can you see the WSS bit in every frame (on a 'scope) or is the packet only sent infrequently?
3. What is the amplitude of the video
4. Is a sound subcarrier present?

Looking forward to your reply

Laurence M0LDZ

vk2crj
Posts: 6
Joined: Thu Oct 29, 2015 8:23 am

Re: Video stream errors

Post by vk2crj » Wed Nov 04, 2015 8:03 am

Thanks for your questions.

1. PAL
2. Every frame, first half of line 23
3. WSS is 0.5V pk-pk (0.3V to 0.8V), video 0.75V pk=pk (0.2V to 1.05V)
4. No sound subcarrier

The source is a JVC GZ-HM670BAA camcorder.

I did get the impression there was some sensitivity to video content.

Regards,

Gary

vk2crj
Posts: 6
Joined: Thu Oct 29, 2015 8:23 am

Re: Video stream errors

Post by vk2crj » Wed Nov 04, 2015 8:05 am

Correction
3. WSS is 0.5V pk-pk (0.3V to 0.8V), video 0.75V pk-pk (0.3V to 1.05V)

M0LDZ
Posts: 73
Joined: Sat Apr 04, 2015 12:59 pm

Re: Video stream errors

Post by M0LDZ » Sat Nov 07, 2015 11:11 am

Thanks Gary

We have been unable to reproduce the issue here although to be fair we don't have your source equipment. It's interesting you suspect video content has an effect though. Is there any way you could attenuate your video by say 10% and see if it makes a scrap of difference?

Thanks

Laurence

vk2crj
Posts: 6
Joined: Thu Oct 29, 2015 8:23 am

Re: Video stream errors

Post by vk2crj » Sat Nov 14, 2015 1:52 am

I tried this, even down to 50% but no difference.

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