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Comment by seanalltogether | Hacker News Reader

Unless I'm very mistaken about modern digital transmissions, cable coming into the house is still based on a broadcast system, which means you're getting everything all the time. The frames are all there for every channel, they're just not being read. I don't know how much processing or memory it would take to read and store frames for surrounding channels to the one you're on, but I imagine its possible.

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While everything is usually on the cable (there are exceptions) the STB only has a limited number of tuners, which means it can't "see" everything at once. The channels that are nearby in number may or may not be on the same physical channel, which would mean the STB is effectively blind to them.

But even in boxes with multiple tuners (DVRs) your solution would require tying up at least three tuners (current channel plus one up and down) which would cut down the number of simultaneous recordings that are possible. I doubt many people would like that tradeoff.

However, the biggest issue is that most boxes simply don't have more than one MPEG decoder in them.

Actually that's a good point, my sky tv box lets me record 6 streams plus watch a channel at once, however i rarely have more then 1 or 2 recordings at a time, so on average i have +2-2 channels available to holder in buffer.

Feel free to find a chipset on the market that can decode hundreds of channels of Full HD H.264 simultaneously...

Only your current transponder.

You wouldn’t have to actually decode it, just receive it all and buffer everything after the last key frame. That eliminates waiting for the next key frame.

receiving it all _is_ the problem. nobody would pay the price for an RF front end with the bandwidth to digitize the entire OTA TV portion of the spectrum. they're spread from 54MHz to 806MHz. that's 752MHz of analog bandwidth. that's huge. (i'm not even sure you could buy that frontend for love or money. ok, maybe you take advantage of the gaps and just have 3-4 frontends. now there's a correspondingly large amount of PCB space taken up, more interference issues, increased defect rate, etc)

Essentially waiting for I-frames as the mini-GP noted it?

Many channels are broadcast, but some are a hybrid. Observe that not everyone needs every channel every second. You can set aside some over-committed bandwidth in an area for the less-in-demand channels and deliver to that area the channels actually desired. This required a change to the CableCard architecture, which has been rolled out for a while now.

Some of the channels I like used to be difficult to tune with my previous cable box, because it would not correctly coordinate tuning with the infrastructure, so I'd have to retune. If I left the box on such a channel and turned it off, the next time I'd use the box the screen would be black.

In the old days all the channels were analog, and used 6MHz each (may vary in your region), and channel changes were much faster.

probably not much because you don't need to decompress them, just keep in volatile memory

> probably not much because you don't need to decompress them, just keep in volatile memory

How do you plan to obtain I-frames without decompressing them?

The decompression could be done lazily when you switch to that channel.

The same way that switching to a channel does it. But instead of waiting for next one to arrive you first scan your 0.5s buffer.

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