[mythtv-users] Comcast HD & firewire

[Scott Alfter]

Preston Crow wrote:
> Just curious; what is the data rate for DVI at 1080i or 720p (whichever
> is greater)?  Does it really exceed disk bandwidth?  And if so, by what
> factor?

1920*1080*3*29.97*8/1e9=~1.49 Gb/s
1280*720*3*59.94*8/1e9=~1.33 Gb/s

A RAID array of some sort might be able to keep up with that, but I don't think
you're going to get sustained performance at that rate from a single disk.

> And while compressing to a regular video format is too CPU intensive,
> what about some very trivial compression?  You could still get
> significant space savings.

Storing component-video data (with chroma subsampling) instead of RGB can cut
your data size in half, but that's still a ton of data to sling around.  You
would probably want the color-space conversion to be done in the capture card.

> I would be happy to set aside 50GB/hour for raw HD with offline
> transcoding if it meant getting all the HD cable channels.

The time it'll take to transcode is not trivial.  Two-pass transcoding of a
165-minute movie in 1080i to H.264, with inverse 3:2 pulldown to restore it to
progressive-scan, took somewhere around 18 hours...and that was on a Core 2 Duo
E6300 (at stock speed).  The same movie, transcoded to MPEG-4 on an Athlon 64
3500 (also at stock speed), took somewhere between 36 and 48 hours to complete
(it was a while ago, so my memory is a bit fuzzy).

The actual resolution of the source video in this case was only 1440x1080, too,
which isn't the maximum possible for 1080i.

> Of course, the real problem is the encryption.

There's already a gadget on the market that'll strip out HDCP, so that's solved:

http://www.engadget.com/2005/07/21/the-clicker-hdcps-shiny-red-button/

Googling for "HDCP stripper" turns up some additional options.

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