June 27, 2007

Secrets of the Cable Universe #1: VOD ffwd/rwd

I've now been working at Comcast for about 6 weeks-ish, and so far, I'm having a blast. Both culturally and technically its a fairly dramatically different environment (along a different axis than the small-to-big transition that AOL was... more on that another time) - which is always fun.

Although I'm finding my skills, talents, and experience are useful (thankfully), the whole Cable/Telecom universe is completely new to me, so the learning curve is both vast and interesting.

In that vein, I though I might share some of the random but interesting technical tidbits that manifest themselves in odd ways, whether operationally or in terms of the consumer experience. Nothing I'll share is (obviously) actually a secret - its either public information and/or subject to trivial induction from public information.

For example, one of the significant features all the Cable operators (MSOs) have introduced over the last few years is Video-on-Demand (VOD). Unlike the "your-movie-starts-every-15-minutes -on-4-different-channels" model that the satellite providers started with, the new VOD systems actually dynamically allocate a unique "physical" channel from your local cable head end when you select a movie. The video asset is then played over that channel which your set top box (STB) is then tuned to automatically, as if it were any other channel in your channel line up.

So the interesting "secret" is that in order to enable fast forwarding (and rewinding) of the assets, each media file actually has additionaly "trick files": copies of the asset at +/- 2X (or whatever the speed multiplier is). When you press the ffwd or rwd button on your remote control while watching a VOD asset, it's actually dynamically switching to another asset at the right time code, and playing from there.

And that is why you (currently) only have one speed for fast forwarding or rewinding: more would have required many more multiple media assets (one at each speed) in the VOD storage systems.

Clever, but strange...

19 comments:

Nate said...

a-HA! I wondered about that the first time I tried to FF through the opening junk that precedes Dora on Nickelodeon. I'd just attributed it to a bug in the still nascent FIOS offering, but now I know better! I don't mind so much the single RW/FF speed, but it is at times inconvenient that VOD takes up one of my two tuners.

Sree Kotay said...

:) Yeah, me too (those opening credits on kids shows are really grating :))

So... I have some thoughts on how to address that more scalably, but obviously, can't comment on any future company plans.

Matt said...

I totally hear where you're coming from.

Prior to joining a VoIP firm, I took it for granted that when I dialed a phone number, another phone rang somewhere in the world and I could talk to a person or leave them a message.

Now that I've learned how the carriers have stitched the whole PSTN together, I'm amazed that the world's simplest use case (dialing a phone) works with such a high degree of reliability.

Trekker said...

Sorry Sree but I'm a very happy Dish customer, j-i-t VOD or not. Apart from having the best HD STB/DVR currently on the market (the Dish ViP622), they've nailed the ethnic programming scene -- several south asian channels, cricket PPV that is not available on any cable/FioS currently.

Sree Kotay said...

Fair - enough, trekker - wasn't try to convert you or anything, just sharing some tech tidbits... :)

Linear programming (or as you non-Cable heads might call them: "channels" :P) is a little different in that regard, and the Cable industry suffers from a bandwidth constraint largely because of the analog content legacy.

Still, there are solutions to every problem and less (overall) channels is clearly one such problem :D

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