Lowest acceptable bitrate for 2 channel AC3

[DRP]

I'm a bit squeezed for space on my latest DVD job here and I'm wondering what is generally regarded as the lowest acceptable AC3 2 channel bitrate? Normally I just stick with 224kbps for AC3 but for this project I could do with having some extra bits in the video instead. I've seen 192kbps on retail DVDs before. What about 160 or even 128? Would I hear the difference?

I've tried 128 & 160 in MP2 and the result was not good. 160 might be acceptable in MP2 if you weren't too fussy but 128 is absolutely hideous with a lot of ringing artifact in MP2.

The audio on what I'm encoding is only actor speech. There is very minimal music. Any recommendations would be greatly appreciated.

[alsyed]

i got to 160kbps in stereo AC3 all the time. I think this is the lowest that i find acceptable. The sound difference between 128kbit and 160kbit is greater than it is between 160kbit and 192kbit. If it is just speech, then 160kbps is fine.

If you have a 5.1 channel encoder, like the one that is in vegas, then you could even do mono though, and you can go down to 96Kbps. Though, mono is unfortunately mono.

[DRP]

Thanks for that. 160 it is then for this project.

Cheers.

[guns1inger]

If it is for you, then acceptable is what you are willing to put up with. There is another thread running at present where the poster is happy with 40kbps MP3 audio and sub-VCD video. Each to there own. If it is for someone else, then I wouldn't go below what the commercial disks use.

Personally, I use 192 for 2 channel, and 384 for 5.1

[reboot]

Do it at 224, then compile and run the whole thing through DVD Shrink

[FulciLives]

I think that the "official" recommendation for 2.0 AC-3 is a bitrate of 192kbps

Most commercial DVD discs use 192kpbs for 2.0 AC-3 although I have seen some use 224kbps and even 256kbps

Almost all stand alone DVD recorders use 256kbps 2.0 AC-3

So I wouldn't go below 192kbps myself.

Personally I always use 256kbps when working with my captures etc.

- John "FulciLives" Coleman

[steve2713]

160 should be fine for your application, just simple voice recording. If it was very 'busy' audio such as an action movie or a sporting event then 160 would be pushing it a bit.

[DRP]

If it is for you, then acceptable is what you are willing to put up with. There is another thread running at present where the poster is happy with 40kbps MP3 audio and sub-VCD video.

Ahem! Yes... well. I'm not even willing to try it to hear what 40kbps MP3 actually sounds like! I think virtually everyone would agree that those specs are too low even if it was nothing more than a videoed lecture taken from a tripod.

[DRP]

Do it at 224, then compile and run the whole thing through DVD Shrink

Are you serious? I'll assume not, but just in case you are I'd be interested in hearing your reasoning why you think shrinking an oversize video would result in better quality than a properly sized video in the first place.

You're saying two generations of encoding will ultimately result in a better quality end result that the same thing encoded once?

[DRP]

I think that the "official" recommendation for 2.0 AC-3 is a bitrate of 192kbps

Yeah I was thinking the same thing

Most commercial DVD discs use 192kpbs for 2.0 AC-3 although I have seen some use 224kbps and even 256kbps

Same here

Almost all stand alone DVD recorders use 256kbps 2.0 AC-3

Thanks for that info. I didn't know that. You have basically confirmed what I was thinking in my own mind which is good. I wasn't that far wrong then. I'll try this one at 160kbps and see how it goes. The job isn't super-critical as far as quality goes, so if 160kbps ends up being unacceptable in this instance it won't be the end of the world. It's a good job to test this out on.

[jimmalenko]

Unless we're talking somewhere in the XVCD/VCD range for your video bitrates (less than approx 1000kbps give or take), IMO you're not gonna gain a helluva lot even with an extra 100kbps or so for the video. I've only even seen 192kbps 2ch AC3, but being a fellow oztralian I normally just stick to 192kbps MP2 anyway.

[DRP]

Not quite that bad but I am in the CVD bitrate sorta range and the audio bitrate I choose will determine whether it's < or > 2000kbps for the video.

2000kbps is a bit of a psychological barrier for me. <2000 will mean I make it CVD resolution. >2000 means I consider using SVCD resolution instead. So yeah there was a little bit riding on the audio bitrate.

As it ended up I used 160kbps for the audio bitrate which meant a video bitrate >2000 but it was only just >2000, so for the sake of full DVD spec compatibility I chose to stick with CVD resolution anyway.