Help with bitrates

[sych0]

Hey guys

I'd like to edit my tivo bitrates. I already have modified them from the originals and am pretty happy with them. What i'd like to do though, is set it up so say on best quality, I'd be able to fit 2 hours with commercials included. Right now, a 2 hour show is about 4.5gb, just a bit too much. Id like to get 2 hrs for best, 3 hrs for high, 4 hrs for medium and 6 for low. Im not sure how the quality would look, but id be interested in trying. The problem is doing the math. Im not sure how each bitrate works. Anyone good at math and familiar with bitrates and such mind giving me some help? Thanks

[sanderton]

1 byte = 8 bits, so 8 megabits per second is 1 megabyte per second on the disk.

So to fit 2hrs on a 4.7Gb DVD, that would be 4.7/(120*60) = 650K/s, = 5,200,000 bits per second. Roughly :)

[sych0]

Hm. Guess i've been out of school too long. That looks fairly simple :) And i knew 8 bits is a byte. Thanks bud

[TRILIGHT]

On a side but related note, bear in mind that "4.7GB" is really just "4,700,000,000 bytes". That really equates to 4.38GB of usable space on your disc. Assuming the SA's record at 192kbps for audio (that's what my DTV unit does. Not sure about SA's), in order to play it safe, I would set your setting as follows...

2hr... 4.80Mbps
3hr... 3.13Mbps
4hr... 2.30Mbps
6hr... 1.47Mbps

[sanderton]

The bitrate you set includes the audio bitrate, IIRC.

[sych0]

Hm...TiVo records audio at 192? That could explain why im getting some bigger than I had expected files. When I transfer mine with tystudio, I use 224. Is 192 dvd compliant or will dvd apps yell at me if I try to add a file with 192?

[TRILIGHT]

Originally posted by sanderton
The bitrate you set includes the audio bitrate, IIRC.

If it's included then these would be your revised numbers, sych0...

2hr... 4.98Mbps
3hr... 3.32Mbps
4hr... 2.49Mbps
6hr... 1.66Mbps

Bear in mind, this is not taking into consideration any space on the disc that you might want to use for menus, etc. or the slight overhead that occurs for the mux. If you're editing commercials out, you're more than fine. If not, you might want to back off these numbers just slightly to give you some breathing room.

As for the bitrate of the audio, the software is not going to bitch at you, sych0. While most audio I've seen tends to be 224, 384, or 448, I've not seen anything complain when using 192. I do not remember the acceptable lower limit for DVD audio. Going lower sounds like crap anyway so I've never bothered.

As for the file sizes, it will have very little to do with the audio bitrate. The audio is VERY small in comparison to the bitrate required for the video. Take a video capture rate of 6Mbps. If you're using 384kbps for audio, you can fit about 90 minutes on a DVDR. Now, if you were to go as far as to cut that audio bitrate in half down to 192kbps, the time you can fit on a disc only increases to just under 95 minutes. Not a big difference as you can see.

[TRILIGHT]

If anyone is wondering where I'm getting my numbers, I wrote a bitrate budget calculator for DVDR a long time ago when I did a lot of capturing. While the spreadsheet specifies only the blue area is for user input, you can change the total DVD size. It defaults to 4.3GB. Change it to 4.38 for the full space on the disc. Here it is, if you want to use it...

[sych0]

Thanks for all your info trilight. I've got the setting in now, and ill see how they work :)

[eastwind]

Also, Toddler posted a set of bitrates from his machine in a different thread. I think it is called 'My TY do DVD process' or something like that. If you do a search on 'hours per DVD' and put Toddler's name in the user box you'll find it.
ew

[TRILIGHT]

Originally posted by eastwind
Also, Toddler posted a set of bitrates from his machine in a different thread. I think it is called 'My TY do DVD process' or something like that. If you do a search on 'hours per DVD' and put Toddler's name in the user box you'll find it.
ew

Here are the bitrates Toddler posted...

Best Quality: 720x480, bitrate 5250000, 2.2GB/hr, 2 hours per DVD
High Quality: 720x480, bitrate 3500000, 1.46GB/hr, 3 hours per DVD
Medium Quality: 352x480, bitrate 2625000, 1.1GB/hr, 4 hours per DVD
Basic Quality: 352x480, bitrate 2100000, 880MB/hr, 5 hours per DVD

Looks like you can actually make your tivo settings a bit higher than a normal capture card would use. Not sure how it is doing it's math for the audio and video together but, from the math and Toddler's settings, I'm sure you'll find something that works for you.