Friday, October 2, 2009

Operational differences

Users of K6BEN/R will have gotten used to how that repeater works - in particular, the use of 2 meter audio for coordination. I used to think it odd that the audio wasn't carried into the repeater as part of the uplink, but having used the repeater, it's clear that it's a fairly useful way to set things up. Someone other than the station sending video can be the source for te audio.

The first iteration of the D-ATV repeater won't have this ability: it will simply retransmit the MPEG TS uplinked by the user station. This means that coordination will have to take place via a traditional 2m or 70cm repeater. One thing that is planned for the future, though, is a shack camera going into an MPEG encoder. But that still would mean it would be a different stream than the one the user is transmitting. So you could watch yourself on TV, or listen to the 2m audio and watch the shack cam, but not both (unless you either decode both at the same time with a computer or multiple TVs).

On the plus side, however, the audio that's part of the MPEG encoding will be vastly higher quality than the narrowband FM we're used to. That may be useful in the context of events. Certainly, the ability to multiplex multiple programs and (when multiple receivers come), uplink multiple simultaneous streams will be very useful for events.

2 comments:

andy said...

Web casting, or broadcasting over the internet, is a media file (audio-video mostly) distributed over the internet using streaming media technology. Streaming implies media played as a continuous stream and received real time by the browser (end user). Streaming technology enables a single content source to be distributed to many simultaneous viewers. Streaming video bandwidth is typically calculated in gigabytes of data transferred. It is important to estimate how many viewers you can reach, for example in a live webcast, given your bandwidth constraints or conversely, if you are expecting a certain audience size, what bandwidth resources you need to deploy.

To estimate how many viewers you can reach during a webcast, consider some parlance:
One viewer: 1 click of a video player button at one location logged on
One viewer hour: 1 viewer connected for 1 hour
100 viewer hours: 100 viewers connected for 1 hour…

Typically webcasts will be offered at different bit rates or quality levels corresponding to different user’s internet connection speeds. Bit rate implies the rate at which bits (basic data units) are transferred. It denotes how much data is transmitted in a given amount of time. (bps / Kbps / Mbps…). Quality improves as more bits are used for each second of the playback. Video of 3000 Kbps will look better than one of say 1000Kbps. This is just like quality of a image is represented in resolution, for video (or audio) it is measured by the bit rate.

Nick said...

Um, you DO get that this is transmitted over the air, right? Nothing whatsoever to do with the Internet...