Originally posted by archiguy
As much as I love this DVR, there's no question it's softening the HD picture (and SD too). That's a shame. There's definite proof of it too.... ATSC HD standard bitrate of 19.2 mb/s takes up about 9 gb/hour of "space". Using the onboard diagnostic screen showing disk size, it's clear (after lots of testing) that an hour of HD recording on the SA8000 only takes about 6 gb/hour on the average, sometimes as little as 5. That means that at least a third of the data is being dropped out, resulting in a softer picture. It appears that the box is only recording HD at around 12 mb/s.
I'd never thought of doing this experiment--thanks!
I notice that they've greatly improved the display of disk space in the diag screens between .151 and .159--this is the first I'd looked at it. I don't actually have any other use for it.
In two samples, I got very different results. (This isn't going to go very quickly, since I'm not willing to delete things without watching them, though I guess I could record stuff that I don't want to watch and delete them immediately
). Ghost Ship
, recorded from HBO HD, came in at 6.8 GB for 95 minutes. That comes out to 9.77 Mbps--not very good. However, an episode of Smallville, recorded from HDNet today, came out at 7.6 GB for 60 minutes, making it 17.29 Mbps, about as good as you're going to practically get from broadcast TV, particularly on cable where all the ATSC padding chaff should be discarded (or never inserted on a cable/DBS only channel. That 19.39 Mbps is a maximum payload for a 6 MHz air channel modulated in 8 VSB. As I understand it, the broadcasters rarely push it to the limit).
The stuff that looks best to me still looks very, very good, which is why I don't think that this box is robbing me of PQ--I recorded a restoration of My Fair Lady
on HDNet Movies that was so sharp and vivid it looked like it was about jump off the screen. I was about to delete it to make space and took a glance at it first; it took my breath away, so I took the time to watch it.
If your system is packing 3 channels per 6 MHz slot and stat-muxing, you could be getting reduced bit rates from some channels because of that. My system has only done that in one slot and only recently--they put Fox HD in with two other channels (PBS and NBC) for some reason, unnecessarily, since there's another slot with only a single channel in it (Showtime is all by its lonesome).
I'm going to continue to take this measurement for a while. I can't wait to see what kind of bit rate I'll get for CSI:CSI this evening.