640 ac3 vs 448 ac3?

[hogger129]

I'm doing some BD backups to a BD9 and am wondering if there's a huge difference. I can do either or but I want to maximize video bit rate.

[jman98]

Most people would not describe the difference as "huge", but there are always some people who swear that they can tell a difference in everything. The odds are quite high that you're not one of those people, so just go with 448.

By the way, DVD doesn't allow for AC3 bitrates over 448 so prior to BD, 448 was as high as AC3 went in the DVD days and I don't recall people back in those times bitching about how "bad" AC3 was.

[Cornucopia]

Although, if the reason for doing it is to save some space, the savings difference between the 2 (a difference of 168.75MB for a 2 hour movie) is probably not worth the loss of quality incurred during the re-encode.

IOW, if this is a BD Backup to HDD, where you have plenty of room, leave it as-is. If this is a BD Backup/Convert to DVD, reduce the bitrate.

Scott

[fritzi93]

If you're using BDRB, 640 kb/s is the default.

What I normally do is first extract main movie with Clown_BD. If the main audio stream is Dolby TrueHD, I use the "extract core audio" option for the audio, which will give you 640 AC3. For DTS, I convert to 640 kb/s AC3, but that's for compatibility reasons. You can extract the DTS core, 768 kb/s from DTD-MA audio.

Either of the above would be better, IMO, than converting to 448 AC3. And if you need to run the result through BDRB to get it down to BD25, well, just tick the do not re-encode audio option.

BTW, lots of times main movie with 640 kb/s AC3 will fit on a BD25 without re-encoding. You save at least a couple GBs by not keeping lossless audio. As to the purists who claim to be able. infallibly, to tell the difference between lossless and AC3 at 640 kb/s...well, I'm doubtful.

[Brad]

not worth the loss of quality incurred during the re-encode.

No need to do a lossy-lossy re-compress when you can do lossless-lossy in most cases.

[jman98]

He's burning to DVD-9 guys. Most of you missed it, but it's where he says BD9 in the original post.

Convert to 448 and see if it makes a big difference to you. I'm betting it won't.

[hogger129]

Thanks guys, I think I will just stick with 448.

[Noahtuck]

Regardless if he is using a dvd5 or dvd9, the size difference between the two final audio is negligible and I doubt there would be any noticeable difference in listening, but as you have basically stated, just use 448, for obvious reasons.

But he does not state what the original audio is, what format, bitrate, what he is using to convert, etc.

OH WAIT!!!

He said bd9 ?!?!

I'm doing some BD backups to bd9

WTF is a BD9 ?!?!?!

[johns0]

He said bd9 ?!?!

I'm doing some BD backups to bd9

WTF is a BD9 ?!?!?!

Bd9=dual layer dvd avchd,around 8.94 gb total.

[Noahtuck]

He said bd9 ?!?!

I'm doing some BD backups to bd9

WTF is a BD9 ?!?!?!

Bd9=dual layer dvd avchd,around 8.94 gb total.

I was thinking that afterwards, basically a bluray on a dvd.....

But then would the lower bitrate required for AC3 on dvd even be an issue here ?
Or the fact that not all Bluray players would play such a disc......

Just checking as their seems to be a lot of different opinions/specs going on here.....

[johns0]

The only reason to use a lower bitrate of ac3 at 448 is to save space which to me is not worth it,better to stay with 640 ac3 rather than saving a measly 150 mb of space,lots of blu-ray players won't play dvd-avchd since it's not a required spec.

Only a few such as sony,phillips will play avchd,not sure of the others.

[Cornucopia]

BD9 (aka BDMV on a DVD9) is a hacked format. The AVCHD spec "legitimizes" it for DVD media, however, because of common consumer DVD spin speeds, the peak legal data limit is 18Mbps. So, if you're "backing up" a BD-50 or BD-25 to "BD-9", even if the space is available, it makes sense to keep the max combined bitrates <=18Mbps, for compatibility-sake. Which means, you may STILL have to down-convert. This has been talked about before.

Scott

[johns0]

99% of all avchd movies to be put on a dvd9 will require down converting or has a bitrate lower than 18Mbps to begin then so unless the movie is 70 minutes or less then bitrate will always be under 18Mbps.

[Hikmet]

If you have enough space on CD, then use 640. If you want a little small size, then 448 is enough. Not a huge differences.