Football time again

Once again BCARES is running a couple of D-ATV cameras at each CU home game. This year there haven’t been any new technical challenges. At events like this, we always station two operators with each camera for safety — one can be looking around if the other is focused on an incident. Here Jack K3UGR and Eric AIØJ keep an eye on the departing traffic after the game (OK, it’s pretty much all departed by now!).


Oh, where did the sound go?

Generally we’ve used Sony cameras in the field for digital ATV, with an HDMI cable running from the camera to the TV modulator.

Last year I got a small, inexpensive CX405 model. I recently tried using it for the Boulder-area weekly ATV net, and no one could hear me. A little digging with the DVB-T test tool revealed that the audio stream was simply absent — no sound was being transmitted at all.

It turns out that newer Sony cameras don’t put out any audio through the HDMI cable (except during playback from a recording). Sony says (as of 2015), “There are no Sony Handycam models that can pass the audio through while recording the video. Again, both video and audio passthrough is only possible when the camera is on playback mode [actually, the issue wasn’t recording, but just live output out the HDMI jack, recording or not].”

This has not been an issue for older models such as the Sony CX430V and AX33.

Also note that the behavior of the Hi-Des modulators is to omit the audio elementary stream from the output transport stream (TS) when no audio is present on the HDMI input. The PID is still listed in the PMT, so the test tool can easily identify it as missing.

Adams County ARES and YouTube Streaming

Last night I gave a presentation on digital ATV to the Adams County ARES (R1 D1) team including a live demo of a portable transmitter and my quad receiver box. It was the 90th anniversary of the first modern TV transmission (7 Sept 1927).

I also talked about streaming TV signals over a network using several different hardware devices and technical approaches. This week YouTube introduced ultra-low latency for live streams. I tested it at home over my wired network, and found that end-to-end latency from camera through RF and conversion to an IP stream, out to YouTube, and back to my browser, all happened within about 2 seconds. That’s fantastic!

In this case I was streaming through a Matrox Monarch HD. I’ve also tested an Epiphan Webcaster X2 but it kept changing the stream latency back to “normal” (15–30 seconds!). I have confirmed with Epiphan that this is an issue that will need to be addressed by a firmware revision.

YouTube live streaming gives us an option when RF alone can’t deliver the picture to a distant command post — provided that we have a suitable internet connection where we operate the ATV receiver. (One catch, however, is that only folks with some type of Google or YouTube account can be invited to watch a private stream, while an “unlisted” stream is accessible to anyone who has the URL.)

See the slides from my presentation: DATV for ARES Sept 2017