football time delay

The following factors are contributing to the delay:

• Round trips to satellites, EM waves traveling at the speed of light. About 1/4 second each round trip. (may be two of them, may be one of these in your radio broadcast as well).
• MPEG encoding, statistical multiplex look-ahead buffer delay (STATMUX processing at uplink center) and MPEG decoding (pipeline). About 2 seconds.
• TiVo's buffering to the hard drive. About 2 seconds.

So, you see, the majority of the delay is the result of processing, about 1/2 second or so is actually due to speed-of-light issues to the satellite.

Indeed, if you compare a regular receiver to a DirecTiVo, the DirecTiVo is about 2 seconds behind the regular receiver due to its disk buffer.

You have probably noticed that when on a news show, they interview someone live via satellite, sometimes there is negligible delay, and sometimes there is significant delay.

When there is negligible delay, it is because their link is an analog C-Band link. The total delay is about 1/4 second from anchor desk to interviewee, then another 1/4 second from interviewee to anchor desk, for a total of about 1/2 second delay. Barely noticeable.

However, when you see a big delay in such a satellite interview, it is because they are using a multiplexed digital (MPEG) C-Band link (which are cheaper and becoming more and more common because of their more frugal use of increasingly limited satellite bandwidth). In this case, the total delay is about 2 seconds from anchor desk to interviewee, and 2 seconds from interviewee to anchor desk. A total of about 4 seconds, quite noticeable to the viewer!

Originally posted by karl_f
I have two Ultimatetv units in rooms next to each other (Family Room / Master Bedroom) and they aren't in sync with each other. They are about a second apart.

Click to expand...

DirecTiVo's, Dish PVR's, and DishPlayers also do this.

This is the reason:

When you first change the channel, the UltimateTV (or other brand of PVR) establishes a disk buffer that is some fixed number of kilobytes.

However, from the moment that buffer is established, it must retain a constant amount of time. If it didn't, the playback would slow down and speed up!

Since the bitrate of any given channels is constantly varying with it's content, the disk buffer must grow and shrink to keep the same number of seconds worth of programming in the buffer.

The bitrate of any given channel can vary from slightly lest than 1 megabits per second to about 5 megabits per second.

So, lets' suppose the initial disk buffer size is 500 kilobytes. After the 500 kilobyte buffer is established, it will grow and shrink so that it always buffers a constant amount of time.

So, suppose you tune to HBO on UltimateTV unit number 1. At the moment you tune to HBO on unit 1, HBO is delivering 3 megabits per second.

Three megabits per second is .375 megabytes per second (3/8 = 0.375) or 375 kilobytes per second.

So, the 500 kilobyte buffer established would contain 1.333 seconds. (500 / 375 = 1.333).

Now, suppose you tuned UltimateTV receiver 2 to HBO at a moment when HBO was occupying 2 megabits per second.

The buffer in this case would contain 2 seconds of video. (2 / 8 = .25) (500 / 250 = 2).

So, in this example, UltimateTV unit 1 would be buffering 1.333 seconds worth of video, and unit 2 would be buffering 2 seconds of video. A difference of 0.666 seconds.

If you could manage to tune both units to the same channel at the very same nanosecond, they would be in perfect sync.

(BTW: I don't know that the buffer size is actually 500 kilobytes, this is a guess, but it is probably pretty close.)