downsample to mono?

[Nucular]

There are some dvds like star trek tng which just have mono sound. It is true that the ac3 data has got two channels but actually it is mono. So I want to downsample the ac3 file to an mono mp3 file. But always when I have ripped the file with besweet or lame to an mp3 I only got an stereo mp3 which has accordingly double the size of a mono file. Who can help me?

[pacohaas]

:readfaq: where's the logfile?

[DJ Bobo]

get it through AZID the following way:

azid -a -c normal -d1/0 -oc filename.ac3 filename.wav

Then encode it in RazorLame to MP3 Mono/

[theReal]

It seems that Besweet when configured to use an --alt-preset mode doesn't add "-m m" to the commandline when you set the encoding mode to Mono.
Is this a bug? I have used --alt-preset 64 and -m m together in Razorlame and the output was mono, even with stereo input, so why doesn't Besweet add the -m m for --alt-preset settings?

However, Mono or Stereo, LAME should still obey the bitrate setting, (unless you were using the standard or extreme VBR setting, where there is no fixed bitrate)

[NuclearFusi0n]

Use joint stereo. ;)

[pacohaas]

Originally posted by NuclearFusi0n
Use joint stereo. ;) not exactly optimal, especially if you know for sure that the source is mono or that the 2 channels are exactly the same. in LAME, mono VBR encoding will save you significant space especially with a 2 hour long track, and mono CBR encoding will be that much better quality than even joint stereo CBR encoding. I just wanted to try to get to the bottom of the problem here, and the logfile will help.

[theReal]

Does the -m m switch work?

I forgot to say, you probably don't even need to seperate the channels and decode only one of them with Azid, like DJBobo wrote. The more important part is that Lame encodes to mono.

I'd use as lame commandline: --alt-preset 64 -m m
That should result in a mono file.

Maybe you also need -resample 48 in case Lame downsamples for the 64kbit bitrate.

[DJ Bobo]

Don't add that --resample 48, since lower bitrates deliver better quality with lower sampling rates. 48KHz is only really OK if your bitrate is 160kbps or higher (80k or higher for Mono). If it goes under 32KHz, choose a higher bitrate, so you're sure to get MPEG1 and not MPEG2 compliant MP3, since MPEG2 compliant MP3 isn't synch with video.