Welcome to Doom9's Forum, THE in-place to be for everyone interested in DVD conversion.

Before you start posting please read the forum rules. By posting to this forum you agree to abide by the rules.

 

Go Back   Doom9's Forum > General > Audio encoding

Reply
 
Thread Tools Search this Thread Display Modes
Old 28th June 2014, 15:29   #1  |  Link
Wowfunhappy
Registered User
 
Join Date: Sep 2013
Posts: 21
ffmpeg: remove audio channel without re-encoding

Hi I like audiobooks and always have. As a result, I have a ton of audiobooks files saved on my computer that I ripped from CD's many years ago. I've long since the lost most of the original CD's.

Being young and stupid, I saved all the these files as stereo rather than mono. In order to save space, I'd like to downmix them to one channel, but I'd rather not re-encode them, partly because I'd like to avoid the inherent quality loss that comes with re-encoding (however small), and partly because the length of each book combined with the size of my library means that a re-encode would actually take a significant amount of time.

I'm assuming that it's impossible to downmix without doing a re-encode—it makes logical sense, and certainly doing '-codec copy -ac 1' doesn't seem—but since I'm pretty sure both the left and right are exact duplicates anyway, would it be possible to simply remove one of the two audio channels? I've done quite a bit of searching on Google and I can't seem to find any information.

Thanks!
Wowfunhappy is offline   Reply With Quote
Old 29th June 2014, 00:01   #2  |  Link
tebasuna51
Moderator
 
tebasuna51's Avatar
 
Join Date: Feb 2005
Location: Spain
Posts: 5,929
You don't say what is the format of your files.

With lossy formats (mp3, aac, ...) you can't downmix without recode.
But, by default, stereo audio with equal left and right channel is compressed using, more or less, the same bitrate than the equivalent mono channel.
Then you can't save space without lose quality.
__________________
BeHappy, AviSynth audio transcoder.
tebasuna51 is offline   Reply With Quote
Old 29th June 2014, 17:00   #3  |  Link
setarip_old
Registered User
 
setarip_old's Avatar
 
Join Date: Aug 2005
Posts: 16,270
@Wowfunhappy

Hi!

Quote:
since I'm pretty sure both the left and right are exact duplicates anyway, would it be possible to simply remove one of the two audio channels? I've done quite a bit of searching on Google and I can't seem to find any information.
I believe you canaccomplish this using VirtualDub...
setarip_old is offline   Reply With Quote
Old 29th June 2014, 18:46   #4  |  Link
raffriff42
Retried Guesser
 
raffriff42's Avatar
 
Join Date: Jun 2012
Posts: 1,376
@tebasuna51 is right, most compression schemes save stereo audio in such a way ("joint stereo") that it doesn't take much more space than mono, especially if there isn't much channel difference content ("separation"). Audiobooks don't usually have a lot of separation.

There's a detailed discussion of this exact question on hydrogenaud.io. They seem to conclude the channels can't be separated without re-encoding - they are multiplexed together at a low binary level.
raffriff42 is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +1. The time now is 13:18.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.