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PVR 150 - Upping res from 480x480 to 720x480 - bitrate?
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Author:  rando [ Wed Feb 28, 2007 12:05 pm ]
Post subject:  PVR 150 - Upping res from 480x480 to 720x480 - bitrate?
Running R5E50 with a pair of PVR 150's (one MCE, one nonMCE). I've bumped my resolution up from the default 480 by 480 (now running 720 by 480) and was just curious what I should be bumping my bitrate up to in order to maintain equivalent quality on my recordings. I'm not completely sure I know how to figure this out.....

Another related Q, I've noticed that in the profile setups there is a bitrate and a max bitrate setting. Do my PVR cards encode varbiable bitrate? I was under the impression that they would have been grabbing shows at a constant bitrate.
Author:  novellahub [ Wed Feb 28, 2007 1:09 pm ]
Post subject: 
I bumped up my bitrates on my PVR-500 after going to 720X480. I don't think there is any definitive guide to what settings to use. I did some test recordings using various bitrate settings to see what was ideal. If I set the bitrate too high, they were not able to play on my Tapeworm Laptop frontend. I think my machine is set up between 4000 and the max of 6000 for High Quality setting (I can verify this later today if you want).
Author:  rando [ Wed Feb 28, 2007 1:38 pm ]
Post subject: 
If you could verify for me that would be excellent. I'm curiuos to see what other people are using. I'd like to find the balance between good quality (the default 480 by 480 was totally acceptable) and a decent filesize.
Author:  ceenvee703 [ Wed Feb 28, 2007 2:40 pm ]
Post subject: 
I use two capture resolutions: 352x480 and 720x480. Both are resolutions that are allowable by the DVD video spec.

Given that 352x480 is a little less than half the horizontal resolution of 720x480, you can get by with half the bitrate to get the same quality recording.

Since 480 is 2/3rds of 720, I believe you'd have to increase your bitrate by 50% to maintain the quality on paper. Some people are pickier than others, though, so you may or may not see a difference. It also depends on what your bitrate was for your 480x480 recordings, and how good or bad the signal is into your card.

The card can do VBR apparently--however there's VBR and there's VBR. It obviously can't do a two-pass VBR and analyze exactly where it can max the bitrate and where it can drop it down. There must be some kind of buffer where it's doing on-the-fly moderate adjustments of bitrate when necessary.
Author:  rando [ Wed Feb 28, 2007 3:02 pm ]
Post subject: 
I'm at work right now and don't have access to my mythbox. So in theory, I would bump the default settings for the bitrate by 50% if I wanted to maintain the same level of quality.

I think I'm starting to wrap my head around things here as far as resolutions and bitrate go. Ultimately it's bytes/pixel that determine how my picture is going to look?

How apparent is the difference in quality between your two settings? And how much filespace do you save by using the lower quality setting?
Author:  novellahub [ Wed Feb 28, 2007 5:49 pm ]
Post subject: 
Here you go:

Name Bitrates (Min / Max)

Default 5000 / 7000
Live TV 4000 / 6000
High 6000 / 8000
Low 2200 / 3000

I don't use the Low setting ever. Most of my recordings use the default profile. All use the 720 X 480 at a 4:3 aspect ratio
Author:  ceenvee703 [ Wed Feb 28, 2007 7:33 pm ]
Post subject: 
rando wrote:
How apparent is the difference in quality between your two settings?


Garbage in garbage out in my case... my Comcast analog cable reception is so poor that it's tough to tell, and I'd prefer to record more programs than to record higher quality (plus it all looks like junk relative to HD anyway).

I record the 352x480 setting at about 4Mbps, which allows me to get a couple hours of video onto a single-layer DVD. I think I have 720x480 for live TV (it makes the on-screen display sharper) but at about 6Mbps, maybe less. The "high quality" setting is 720x480 at 8Mbps.
Author:  opel70 [ Thu Mar 01, 2007 9:15 am ]
Post subject: 
novellahub wrote:
Name Bitrates (Min / Max)

Default 5000 / 7000
Live TV 4000 / 6000
High 6000 / 8000
Low 2200 / 3000

I don't use the Low setting ever. Most of my recordings use the default profile. All use the 720 X 480 at a 4:3 aspect ratio

Pretty much the same here except I have my Default set the same as LiveTV at 4500/6000. The help text that 2200 results in ~1GB / hour is pretty accurate.
Author:  rando [ Thu Mar 01, 2007 9:32 am ]
Post subject: 
So, I've bumped up my bitrates, and am now seeing the "full buffer" errors again.... It's unrelated to the topic of this post, so I'm going to start a new thread rather than derailing this into an unrelated discussion......
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