How to find out what capture cards support what bitrates?

[cmcquistion]

Got a weird situation. My BTV Server has a Hauppauge PVR-500 and an ATI Theatre 550. I changed my Recording Qualities to this, for some test recordings, using variable bitrates:

Best 6000-9000 kbps
Better 5000-8000 kbps
Good 4000-7000 kbps
Fair 3000-6000 kbps

All used 720x480.

When I did a 5 minute test recording, using each profile (using only the ATI Theatre 550 card), the Best, Better, and Good recordings were all very close to the same file size (~240 MB). Only the Fair quality was significantly different (~127 MB). Is this an issue with BTV or with limitations of the card (or drivers) for what bitrates it supports? I can't seem to find very solid information on this, from ATI, but I seem to recall reading somewhere that this card likes to work with only certain bitrates. If I recall the discussion, correctly, someone claimed that it only used bitrates that were a multiple of 1000.

Any ideas?

*EDIT* I may be running into bugs with the program, also. I am setting up another round of test recordings and it keeps resetting my "Good" program to "Best" Quality, for some reason. It doesn't do it with the other recordings and this time I'm testing, using the Hauppauge tuner, instead of the ATI tuner. If I tell this particular recording to use the ATI tuner, it still resets it to Best quality???

[dallas2727]

I use a 10000 bitrate. Hauppagues sites lists bitrates up to 12000 for the 250, I would assume the 150 is capable of the same.

[cmcquistion]

I repeated the tests with the Hauppauge card and got the results I expected. I guess the issue is with the ATI card, or it's drivers, or how BTV interacts with it.

5 Minute Clip, each:

Best ~237 MB
Better ~199 MB
Good ~164 MB
Fair ~127 MB

[Fonceur]

If you plan on making "standard DVD's" using editing software, you might want to limit the maximum bitrate to about 8.5k, otherwise the software might complain of exceeding the DVD specifications...

[cmcquistion]

I thought the DVD spec included variable bitrates up to 9K? Does 9K include video and audio or something?

[Fonceur]

Originally Posted by cmcquistion

I thought the DVD spec included variable bitrates up to 9K? Does 9K include video and audio or something?

Indeed 9k is the combined video + audio, so if you put the video at 9k already, you're going out of spec...

[cmcquistion]

Ok, then I should be able to drop the bitrate down to about 8750 or so, since I'm using 224 for the audio.

I will change my settings and do some more tests in a few days. I'm going to be doing a bunch of changes to my hardware, anyway.