reencoding 6-channel ac3 to lower bitrate

[dragon101]

I have a 369mb ac3 is there any way to re-encode it inoto a 250mb ac3?

[4lex]

AFAIK AC3 is pretty well compressed already, a 6ch (5.1) stream being only 384 kbps, which is only the same as 3 stereo mp3 streams, ie 6 channels.

Fair do's you do get some 448 kbps streams, but you see the point. I reckon you'll either have to put up with it or go to two channels MP3 or similar.

Alex

[MaTTeR]

Why not decode the AC3 to seperate WAV files and then re-encode to something like 256kbps AC3 using SoftEncode...you will be more than happy with the quality. Trust me:)

If you'd rather not go that router for whatever reason, have a look at Vorbis audio. Vorbis supports "true" VBR resulting in smaller file sizes over MP3. Re-encoding the AC3 to a lower bitrate is a much better way to go over using something like Vorbis or even MP3 IMHO.

[kilg0r3]

@matter
how low in bitrate can you go for a 2ch sourround encoded ac3 file?
and, do you know of guide or downloadable manual that explains the options in softencode?

[DSPguru]

Originally posted by kilg0r3
@matter
How low in bitrate can you go for a 2ch sourround encoded ac3 file? that's not a wise action. if you re-encode to a 2ch soundtrack, you better encode to ogg (or mp3).

[MaTTeR]

I agree with Dg on this one. Transcoding your 2ch(DPL) to anything other than Vorbis or MP3 may not be a good idea.

My comment above about transcoding the AC3 to a lower bitrate(256kbps) AC3 only applies for 5.1 streams.

[kilg0r3]

thanks :) souuu much

[DSPguru]

you can easily reencode a 5.1AC3 to a lower-bitrate 5.1AC3 with The AC3Machine together with BeSweet v1.4b1.
get if from my webpage :o.

[nah]

Yeah, cool,

1h30 AC3 384k to 224k with Celeron II 1.2G @ 1.448 Ghz 512Mb
SoftEncode : total nearly 1 hour
AC3Macine : nearly 15 min

--> up to 4 times faster.
Quality ? I have only 2 PC multimedia speakers :(

[canadian_fbi]

wow, that's quite the speed increase. with this tool and the xcd project, we could be looking at easy to make, high quality 800 mb 1-cd movies with 256 kbps dolby digital audio :)

although i think that someone does need to test the quality of this encoder at 256 kbps (and other bitrates) much like the test that was done a while back with softencode (i think) to establish that 256 was an acceptable bitrate for AC3. i can't do this myself for two more weeks until i get my receiver and whatnot here... i'm moving and my stuff's currently spread over four states :(

[KeithXP]

Help,

I am backing up Rules of Engagement. I have demux the ac3 track and it comes out unusable in DVDMaestro because the of variable bitrates. So, I demuxed the ac3 track using SmartRipper and the track has too high of a bitrate to fit with my video.

1) Is there a way to lower the bitrate on this 6 channel ac3 track?
2) Is there a way to demux the track at a CBR instead of the VBR?

Help,
KeithXP
:confused:

[cult]

1)to lower the bitrate of ac3-softencode
2)nandub

[KeithXP]

Thanks cult,

It took me days to find this Soft Encode. I have tried loading the .ac3 file in all the ways in Soft Encode with no luck. I must be doing something wrong.

Is there a way to load my high bitrate .ac3 file in Soft Encode and convert it to a lower bitrate? If so, do you care to explain how, step by step?

Help,
KeithXP

[theReal]

Use AC3machine for the reencoding. It's free and it's pretty easy to use. I think it's somewhere on Doom9's download site.
It additionally needs the besweet executable to work (also on Doom9's site).

[scryber]

I have a 6-channel ac3 file that is just a little too large to fit on a DVD-R with the main movie m2v file. The 2-ch ac3 file fits, but I'd rather have 6-ch.

Is there a way to resample the 6-ch at a lower bitrate? I'm assuming that converting the 6-ch to wav throws away the 6 channels and reduces it to two, so that is one step to avoid.

thanks for the help!

[DSPguru]

use Soft Encoder :
http://www.doom9.org/transcode_ac3.htm
or AC3Machine :
http://www.doom9.org/ac3machine.htm

[scryber]

When I try to select the Input ac3 file with AC3Machine, none of my ac3 files show up in the Open window. wav files do (when wav is selected as the file type), but ac3 don't.

So I typed the file path manually and did the rest of the settings. At the end of the transcoding, the log file reports "Actual Avg. Bitrate : 128kbps" -- I set the bitrate at 224. And when I try to import the new file into my authoring program, it gives an error saying it isn't an ac3 file.

Any ideas?

[DSPguru]

Originally posted by scryber
When I try to select the Input ac3 file with AC3Machine, none of my ac3 files show up in the Open window. wav files do (when wav is selected as the file type), but ac3 don't.http://forum.doom9.org/showthread.php?s=&threadid=31890&highlight=ac3machine

So I typed the file path manually and did the rest of the settings. At the end of the transcoding, the log file reports "Actual Avg. Bitrate : 128kbps" -- I set the bitrate at 224. And when I try to import the new file into my authoring program, it gives an error saying it isn't an ac3 file.

Any ideas? http://forum.doom9.org/showthread.php?s=&threadid=32277&highlight=ac3machine

[MaTTeR]

Admitingly I was skeptical of AC3 Machine at first when I seen how fast it was and was worried about the quality. Now months later I have to say the speed is incredible and I use it for most drama type movies with little action. I have not did a quality test and compared it to SoftEncode but for most of the low action drama type movies, using AC3Machine/AC3Enc/BeSweet(not sure what to call the actual app) @ 224/256kbps is highly recommended from me:D

DG is correct, transcoding a 2/0 AC3 to lower bitrate AC3 is a bad idea, I'd just use Vorbis for such a thing.

I can't wait until MP4 finally becomes somewhat flexible so we can transcode an AC3 to a lower bitrate AAC inside of an MP4 container*sigh*

[MaTTeR]

Again, here's a sample of the speed to expect. Dual XP 1600's and 2 7200RPM drives were used for this very very long movie(Stephen Kings Red Rose). Movie is (254mins) 4hours and 14mins long!

BeSweet v1.4RC7 by DSPguru.
--------------------------
Using azid.dll v1.8 (b825) by Midas (midas@egon.gyaloglo.hu).
Using AC3enc.dll v0.2 by Gerard Lantau & Dg (http://ffmpeg.org).

Logging start : 09/09/02 , 12:16:39.

C:\Program Files\BeSweetv1.4RC7\BeSweet.exe -core( -input d:\DIvX RIPs\Red Rose\RR.FF AC3 T01 3_2ch 384Kbps DELAY 0ms.ac3 -output z:\DivX\ROSE_RED_DISC_1\rr_224kbps.ac3 -logfile C:\Program Files\BeSweetGUI0.6b59\BeSweet.log ) -ac3enc( -b 224 ) -profile( ~~~~~ Default Profile ~~~~~ )

[00:00:00:000] +------- BeSweet -----
[00:00:00:000] | Input : d:\DIvX RIPs\Red Rose\RR.FF AC3 T01 3_2ch 384Kbps DELAY 0ms.ac3
[00:00:00:000] | Output: z:\DivX\ROSE_RED_DISC_1\rr_224kbps.ac3
[00:00:00:000] | Floating-Point Process: No
[00:00:00:000] +-------- AZID -------
[00:00:00:000] | Total Gain: 0.0dB, Compression: None
[00:00:00:000] | LFE levels: To LR -INF, To LFE 0.0dB
[00:00:00:000] | Center mix level: BSI
[00:00:00:000] | Surround mix level: BSI
[00:00:00:000] | Dialog normalization: No
[00:00:00:000] | Rear channels filtering: No
[00:00:00:000] | Source Sample-Rate: 48.0KHz
[00:00:00:000] +------- AC3ENC ------
[00:00:00:000] | Bitrate method : CBR
[00:00:00:000] | AC3 bitrate : 224
[00:00:00:000] | Channels Mode : 5.1
[00:00:00:000] | Error Protection: Yes
[00:00:00:000] +---------------------
[04:14:20:928] Conversion Completed !
[04:14:20:928] Actual Avg. Bitrate : 224kbps
[00:35:57:000] <-- Transcoding Duration
Logging ends : 09/09/02 , 12:52:36.