BATC Forum

Hi all,
With GB3NQ now HD and working well, throwing everything at it as far as video is concerned and with lots of tests and tweaking, there is just a small chance of lockups in the Portsdown and Ryde receivers when the content hits the 'no more nulls' limit in the transmitted signal. With the beacon video seen via the streamer ( also in HD ) transmitted at 12:00 and hourly until 21:00 you can see this when the video has tree ferns etc. and a pan across them. The beacon video was made to demonstrate places in Cornwall and the aerials etc. while pushing the system.
The question is that is there anything that could be done to make the Portsdown/Ryde ignore the lack of nulls and continue like a satellite receiver does? If so then it should probably be able to be enabled or not via the menu. The lockups are for a few seconds while the satellite receivers missing these few frames is not noticable.
Most people will monitor the repeater via a satellite box but when transmitting may use the stream feed which is a Ryde so you get the Awaiting GB3NQ reception screen etc.

The repeater output is on 1316MHz and the beacon video is 30 minutes so if you want to try receiving pictures during good conditions we would like to hear reports.
For more info you can see http://gb3nc.org.uk/

Martin G8LCE

Martin

There are 2 issues here.

The root cause, which you gloss over, is that the transmitter is not transmitting a valid transport stream (and hence a valid video signal) during the periods of high picture detail. You mention the lack of nulls - if the transport stream has exactly the maximum bitrate, there will be no nulls and the video will be perfect. The problem is that the encoder is outputting a transport stream at higher than the maximum bitrate, and the transmitter is unable to transmit it all. It doesn't transmit any nulls because it is doing its best, but cannot squeeze any more bits down the pipe, so drops some.

It is very difficult to overcome this problem with encoders that are affordable for amateurs; we are struggling with the same issue on GB3HV, and have come to a compromise where it behaves for 99% of the time, but occasionally cannot handle noisy or complex pictures.

The second issue is how the receiver copes with the corrupted video it receives. Most set-top boxes use a hardware video player that is designed to handle corrupted video with least disturbance to the viewer. Both the Ryde and the Portsdown use the VLC software video player by default. We have spent many hours experimenting to find the best settings for VLC.

My only suggestion would be to try the Ryde "hardware decoding" option, which you can enable by directly editing the Ryde config file. Failing that, if you can find a better video player that works on a Raspberry Pi, I'd be happy to try to add it to Portsdown as an option.

Dave, G8GKQ

You can improve matters somewhat if you increase the buffers at the penalty of longer latency. It depends what you want. Always a compromise.

Mike