What bitrate for 2.0 AC3?

[trg100]

Just a quick question and forgive me if this is lazy of me. How lo can I go with the bitrate for a 2-channel AC3? 192kbps? 128kbps? 96kbps?

[frank]

All DVDs use 192 kbps on 2/0 tracks. Recommended by Dolby.

[DJ Bobo]

192kbps is actually minimum to get full bandwidth (=frequencies up to 20KHz)
If you can use a higher bitrate, don't hesitate, it will give you slightly better quality.
For example, ADV Films uses 224kbps for 2.0-AC3 in their Anime DVDs, FUNimation uses even 256kbps for 2.0-AC3 in their Dragon Ball Z DVDs.

But you shouldn't encode to AC3 anyway because:
1) encoding is too slow in comparison with MP2- & MP3-encoding.
2) if you're planning a DivX-Rip, MP3 is better
3) if you're planning to author a DVD, MP2 is allowed and will give you excellent quality starting from 224kbps (well, 192kbps is OK too, if you're not that audio freak)
4) you must know what you're doing, since AC3 has some strange encoding techniques, that make sound less loud (eventually). On the other side, MP2 & MP3 keep the volume as is, which is quite an advantadge IMHO.

[Galmok]

I have trouble creating an AC3 2.0 from an AC3 5.1 (3_2). All I get is silence. I am using besweet 1.4b12. Are my switches wrong or is ac3 2.0 not supported (though it should be acording to dspguru.doom9.net)? About the overflows

C:\download\divx\BeSweet>BeSweet.exe -core( -input "E:\fs1\fs 1x01 AC3 T01 3_2ch 448Kbps DELAY 0ms.ac3" -output "E:\fs1\fs 1x01 AC3 T012_0ch 192Kbps DELAY 0ms.ac3" ) -azid( -s surround2 ) -ac3enc( -b 224 )

BeSweet v1.4b12 by DSPguru.
--------------------------
Using azid.dll v1.8 (b825) by Midas (midas@egon.gyaloglo.hu).
Using AC3enc.dll v0.1 by Gerard Lantau & Dg (http://ffmpeg.org).

[00:00:00:000] +------- BeSweet -----
[00:00:00:000] | Input : E:\fs1\fs 1x01 AC3 T01 3_2ch 448Kbps DELAY 0ms.ac3
[00:00:00:000] | Output: E:\fs1\fs 1x01 AC3 T01 2_0ch 192Kbps DELAY 0ms.ac3
[00:00:00:000] | Floating-Point Process: No
[00:00:00:000] +-------- AZID -------
[00:00:00:000] | Output Stereo mode: Dolby Surround 2 compatible
[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 : 2.0
[00:00:00:000] | Error Protection: Yes
[00:00:00:000] +---------------------
[00:48:06:944] Conversion Completed !
[00:48:06:944] Actual Avg. Bitrate : 224kbps
[00:05:11:000] <-- Transcoding Duration

[pacohaas]

@Galmok: you've gotta read the FAQ's and stuff at the top of the forum, it saves all of us a lot of time, thanks.

[Galmok]

pacohaas: You imply that I did not read the FAQ, but I did. The FAQ does not mention anything about the beta release of besweet not being able to encode ac3 2.0 (as is should reading the release information for besweet 1.4b12) nor does it give any examples for the options required to do so. Therefore you apparently don't know what you are talking about (sorry to say so). If I am wrong, please correct me. If not, can you actually help?

[pacohaas]

i guess it's a bit confusing, but in "Sticky: Read before reporting BeSweet bugs!", # 19:19 - 2.0 AC3 streams created by ac3enc seems to be broken. only 5.1AC3 streams came out valid. and unless something has happened that I don't know about, the ac3enc dll hasn't been updated so this is still an issue.

[Galmok]

I guess it is a bit confusing (for you that is) as the item # 19 you are referring to is for BeSweet v1.3 and NOT v1.4b12. If you had taken the time to check dspguru.doom9.net (http://dspguru.doom9.net) you would notice that AC3 2.0 has been added to BeSweet v1.4b12.

If for some reason that is not correct, the error lies with DSPGuru and not me. He should not have added AC3 2.0 to the list if it is a non-working addition.

If AC3 2.0 encoding is present (as is clearly stated), I still would like to know how to make it work.

[DJ Bobo]

@ Galmok
You're only wasting your time, use MP3 or MP2 instead.

[DSPguru]

Originally posted by Galmok
I guess it is a bit confusing (for you that is) as the item # 19 you are referring to is for BeSweet v1.3 and NOT v1.4b12. If you had taken the time to check dspguru.doom9.net (http://dspguru.doom9.net) you would notice that AC3 2.0 has been added to BeSweet v1.4b12.

If for some reason that is not correct, the error lies with DSPGuru and not me. He should not have added AC3 2.0 to the list if it is a non-working addition.it might be confusing. here are the facts :
BeSweet v1.4b12 do supports encoding of 2.0AC3, using ac3enc.dll, but, it seems that ac3enc.dll produces invalid 2.0ac3 streams.
i might be fixing up the code of ac3enc.dll, as a service to my users, but ac3enc producing invalid streams is not an "error lies with DSPguru", but a bug introduced by ac3enc developers.

if you feel like bitching about ac3enc, i would adise that you send an email to : ffmpeg-devel@lists.sourceforge.net .

Originally posted by DJ Bobo
@ Galmok
You're only wasting your time, use MP3 or MP2 instead. agreed.

[Galmok]

Thanks, DSPguru, for setting things right, and welcome back :-)

Now, the main reason I wanted AC3 insted of mp3/mp2 is that AC3 can be transported without any modification via S/PDIF to my surround amplifier.

I didn't know the ffmpeg guys are responsible for ac3enc.

[DSPguru]

it would be really great if you'll mail them your logfile and impression of the 2.0ac3 product.
i would have done it, but have no time currently.

[wanton]

It seems that ffmpeg encoder was 2 channel only ac3 encode before ac3enc.c reached v1.7 and not much have changed since new v1.7 and v1.9. Encoding two channel ac3 must have worked in version v1.6 or earlier.

[DSPguru]

thank you for this input.