Why is the AC3 limit 384Kbs?

[jweaver]

I need to convert some MKV/MP4s from AAC to AC3 and was recommended to try Avidemux.

It looks ideal, but I am a bit worried that i can only encode AC3 at 384KBs.. Unless I am missing something, even DVDs are encoded at 448kbs.. Why is there a limit of 384K, when 640k is possible?

This is a shame, as should I want to retain the quality, I am forced to re-encode at 384K... Is there any way to open up more speeds?

Jon

[mean]

448 is dts, DVD's ac3 is 384 if i'm not mistaken

[jweaver]

Don't think so

http://en.wikipedia.org/wiki/Dolby_Digital#Dolby_Digital

448 is DVD.. 384K was from the Laserdisk era... So unless i am missing something,you can't even encode AC3 at the standard DVD quality.. And certainly not Blueray (640K)

Is there a way to get the author to add this functionality? It would surely make sense for someone to choose the bitrate of AC3, right up to the maximum allowed (640K)?

Jon

[jweaver]

I just did a random poll on a number of movies that I have with AC3. They are either 448K or 384K..

It just seems a huge shame to not allow AC3 encoding at 448 (or greater).. I really hope the developer is still evolving this application and is willing/able to add 448K, or I need to find something else and I really look the look of this tool!

Jon

[mean]

Workaround : i think if you save the project and change 384 to 448 in it it will work
(its a simple text file)

[jweaver]

Workaround : i think if you save the project and change 384 to 448 in it it will work
(its a simple text file)

Interesting.. i will give it a try later.> I am just encoding a movie in a range of Bitrates to see when/where/if I can spot the difference.

Editing a project each time will be a pain. BUT.. Avidemux seems to do what it does better and easier than anything else, so it will be worth the extra effort....

Does anyone know how to contact the developer and ask for this feature to be added/enhanced? It should be a tiny change!

Jon

[jweaver]

Unfortunatly, the Project workaround doesn't appear to work.

I setup the GUI with the parameters that I normally use and save the project, and this gives

#PY  <- Needed to identify #
#--automatically built--

adm = Avidemux()
adm.loadVideo("F:/DOWNLOADS/Completed/STAR WARS SAGA 1977 2005 BluRay 1080p QEBS5 AAC51 PS3 MP4-FASM/Star_Wars_Episode_IV_A_New_Hope_1977_1080p_BluRay_QEBS5_AAC51_MP4-FASM.mp4")
adm.clearSegments()
adm.addSegment(0, 0, 7484769000)
adm.markerA = 0
adm.markerB = 7484769000
adm.videoCodec("Copy")
adm.audioClearTracks()
adm.setSourceTrackLanguage(0,"unknown")
adm.audioAddTrack(0)
adm.audioCodec(0, "Aften", "bitrate=384", "mode=0");
adm.audioSetDrc(0, 0)
adm.audioSetShift(0, 0,0)
adm.setContainer("MP4V2", "optimize=0", "add_itunes_metadata=0")

I then change the relevant line to:

adm.audioCodec(0, "Aften", "bitrate=448", "mode=0");


When I open the project, the GUI doesn't even change and Audio shows "Copy", but I went ahead and saved the file..

And the Audio changed from

Audio
ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 2h 4mn
Bit rate mode                            : Variable
Bit rate                                 : 375 Kbps
Maximum bit rate                         : 439 Kbps
Channel(s)                               : 2 channels
Channel(s)_Original                      : 6 channels
Channel positions                        : Front: L C R, Side: L R, LFE
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Stream size                              : 335 MiB (11%)
Language                                 : English
Encoded date                             : UTC 2011-10-06 16:32:14
Tagged date                              : UTC 2011-10-06 16:32:23

to

ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 2h 4mn
Bit rate mode                            : Variable
Bit rate                                 : 375 Kbps
Channel(s)                               : 6 channels
Channel positions                        : Front: L C R, Side: L R, LFE
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Stream size                              : 335 MiB (11%)
Encoded date                             : UTC 2014-02-18 22:15:44
Tagged date                              : UTC 2014-02-18 22:17:39

So it hasn't worked.. Any other suggestions? I am absolutely gutted.. Avidemux is exactly what I want and it does what it does perfectly.. But I don't want to re-encode 50% of my movie collection to sub-DVD quality audio..

Jon

[AQUAR]

I tried that work around and got AC3 with a 448 Kb bitrate.
So it did work.

Did you use a plain text editor (to avoiding adding embedded formatting)?   

[jweaver]

Weird.. I tried a bunch of times.. I used "Getdiz" which doesn't add any formatting.

When you did it and opened the Project, does the Audio change from "Copy"? And if not, when you go into the Config can you see 448 on the GUI...

Forget that.. I just tried again, and this time the GUI showed the correct Audio mode, and although "config" shows the settings 56K, it did the encoding at 448K..

Appologies for that.. I tried many times and got the same result each time so clearly I was doing something wrong.. Where do we go from here.. This appear to work for sure, but its a bit of a pain.. Do you think the developer reads these posts and is likely to change anything?

I have found another app called "Mediacoder" which works and allows speeds >384K.. But its quite complex and has a lot more settings and therefore its easier to mess it up.. I would really like to make Avidemux my default app...

Jon

[AQUAR]

@ jweaver.

Well the developer has already replied to your post!

Will he add the option for 448 in the GUI - I'll be presumptious and say "most likely - probably - Yes".
Yes - because the code change to avidemux would be minor.

Maybe others can lend support for including the 448 Kb bitrate!
Personally I can't hear the difference, but my hearing is not that of a young person. 

[jweaver]

Ohhh. .So "Mean" is the Developer? I just assumed he was the Moderator..

Sorry Mean, didn't intend to question your answer.. Hope no offence is caused.

It would be great if you could add support for higher bitrates.. I will keep an eye on the news page to see if any new releases come out, but for now, I will go down the "Project" route..

As for the quality difference between 384 and 448, there is probably none.. But I have spent a small fortune on my home cinema setup and don't really want to go backwards on the quality front.. When you consider that I am trying to convert AACs, which bit for bit is higher quality, I want to ensure that I am not introducing any unnecessary losses into the equation.

Jon

[AQUAR]

I think the bitrate limitation harks back to the days of video DVD media.
DVD's often use 192 Kb for AC3 audio to help keep a check on peak bit rates.
Some dvd players would 'choke" if you used a high audio bit rate.

Not so much an issue these days with modern delivery systems.

Question is, why recode AAC to AC3 if quality is the objective?
Likely to lose more in going from one lossy compression to another lossy compression than that from the minimal bitrate difference.

 

[Jan Gruuthuse]

Revision 9022 [ac3/lav] Bump max bitrate to 448
source: http://svn.berlios.de/viewvc/avidemux/branches/avidemux_2.6_branch_mean/?view=log

[jweaver]

I think the bitrate limitation harks back to the days of video DVD media.
DVD's often use 192 Kb for AC3 audio to help keep a check on peak bit rates.
Some dvd players would 'choke" if you used a high audio bit rate.

Not so much an issue these days with modern delivery systems.

Question is, why recode AAC to AC3 if quality is the objective?
Likely to lose more in going from one lossy compression to another lossy compression than that from the minimal bitrate difference.

Unfortunately, my home cinema setup does not support AAC, so if have no choice really.. Whilst Quality is my objective, Convenience is higher up the list and I just want a format that will play.. But I don't want to short change myself going to 384, when 448 is an option.

Thanks Jan for making this change.. I really appreciate it

Jon

[AQUAR]

Mean hasn't compiled those latest code revisions as yet.
So keep an eye on the nightlies.
They are updated quickly so the wait will be short.