4+hour DVD9, lower audio bitrate for better video?

[sdsumike619]

Hi all, I have a 4 hr, 7 min, 30sec video for DVD9 replication. Using a calculator I determine that with 10MB space for extra content, this yields:

4228kbps for the video using 256kbps AC3
4260kbps for the video using 224kbps AC3
4292kbps for the video using 192kbps AC3

If my audio is regular 2.0 channel being encoded from a DV AVI source, would it benefit my video encode to use 192kbps for the AC3? Or will the gain in video quality be negligible by going down to 192kbps? I should also mention that the video is simply a music instructor talking and performing on a black background for the entire duration.

Here's another question, how much space should I really allow for the extra content? is 10mb enough? There won't be any other files in folders on this DVD. Just the menus which will be still menus...

Thanks!

[guns1inger]

256 kbps is the sweet spot for 2 channel audio. After that it really depends on the quality of the recording and the need for audio fidelity as to whether or not a lower bitrate is appropriate. If you are recording only with the camera mic then 192 may well be all you need.

I am also assuming that these are average bitrates for a VBR encoding, and not THE bitrate for a CBR encoding. It is a VBR encoding, I would probably take the middle ground and go for 224 kbps for the audio, as VBR encoding of a mostly static video should give you reasonable video even at that bitrate. If you are encoding CBR then you will have to give it all you can, and even then you may suffer somewhat for it.

[lordsmurf]

If this is 720x480 content, I think you're putting too much on a disc.

[sdsumike619]

Yeah I know I am, It's 7.5 minutes over 4 hours and but like I said it's not a hollywood epic, and it's still clear video. I just wanted to know if using 192 as opposed to 224 or 256 would make the video look any better at all..

[guns1inger]

The difference would be marginal for the video, but more likely to be noticeable on the audio side. Why not just encode a 5 minute sample at each bitrate (both audio and video) and see what works ?

[sdsumike619]

I'm not even sure really. I'm going to be using Adobe Encore CS3 for the authoring project. It has an auto transcode setting which is recommended and then it also has options to modify the transcode settings as well. I will probably just go middle of the road with 224kbps. The only things on the video are guitar and voice so I'm probably being overly critical about it..

[lordsmurf]

Just do the 256k audio. The video will suffer either way (unless it's motionless), but don't make the audio suffer too.

I've not used Encore CS3 just yet, not had a project on it. Absolutely in love with Premiere Pro CS3, on the other hand, much improved over past versions.

[sdsumike619]

Ok; thank you

[jman98]

Lowering the audio bit rate to "improve video quality" is akin to deciding to spend $2000 for an HD TV and sweating over whether it's worth it to drive to another store because you might save 5 cents on the price. In other words, the audio takes up such little space that even if you lower the bit rate, you're not going to gain enough to make any difference on the video side. You won't be able to see any difference at all in the video at the bit rates you quoted. Do a test encode at the lowest and highest bit rate you listed and you'll see that they look the same to you. You really have to get into bit rate differences in the thousands before you can start to see differences.

[solarfox]

Here's my take on it, for what it's worth...

In the end, which is more important for this particular programme -- the video, or the audio? If this is a musical performance which you want to sound as good as possible, and the video quality isn't so critical (i.e. there's no fast motion, you don't need to be able to read anything the music instructor is writing on a blackboard behind him, or anything like that), then what I would do is encode the video as half-D1 (352x480) VBR with an average around 4Mbit/sec, and encode the audio as at least 256Kbit AC3. (Depending on the kind of music, I might even go to 320Kbit just to insure there's no slurring of the high frequencies -- but then, my ears seem to be unusually sensitive to that sort of thing, so your mileage may vary. )

If, on the other hand, this is an instructional video where you need to have a clear view of some written text on a blackboard or the instructor's sheet music, and the actual audio quality isn't so critical (because it's mostly spoken-word stuff, or the recording is less than ideal to begin with due to poor acoustics), I'd go full-D1 VBR @ 5Mbit/average and cut the audio to 160Kbit AC3.

[mats.hogberg]

160 or 256 or 448 kbps or whatever audio - It will make absolutely no visible difference to the video quality, unless we drop video down to the 2-3000 kbps zone. But it will make an audible difference to the audio quality.

/Mats