Compressing
Audio for your MPEG 1/2
Most of you will be wanting to know about
encoding audio for MPEG 1 but this guide is also useful for MPEG2 stuff.
MPEG audio
For most people the choice of audio compression
will be no choice at all. Mpeg-1 layer 2 audio is what ErMaC recommends
in his guide and indeed it is the standard... you should never use
Mpeg1 layer 1 audio because it's seriously old and seriously crap (it's
pre-vcd which is pre 1993). So, mpeg1 layer 2 it is.
Mind you, it is possible to use MP3 audio in your
mpeg video files. The only problem with this is that they aren't
compatible with hardware playback - so vcds, dvd players and hardware
mpeg players will all have trouble with mp3 audio but in terms of
playback in software mode there is no problem whatsoever in using an
MP3 stream for the audio (except really really old pcs like P100s etc
might get lagged).
[note - do not use mp3 for convention
submissions as they often use hardware players]
The choice is yours - I'll describe how to do
good encodes with both mp2 and mp3 audio but you need to decide whether
you want to have the video more compliant (which, if you are using
ErMaC's TMPGenc method it wont be anyway) or smaller/better quality
audio-wise. If you are doing an MPEG2 video file for a DVD master then
you'll have to choose mpeg layer 2 audio (unless you are DVD authoring
where you could possibly use WAV PCM but if you know much about
authoring then you know more than me already)
For this, the program used will be TMPGenc which you should know about
from ErMaC's guide.
mp2 - TMPG's audio encoding capabilities
are ok.. but they're nothing special. There is a better way to get
quality audio when encoding with TMPG using an addon program called tooLAME. This is a
simple .exe file that you can put anywhere on your computer. Once
you've extracted it, load up TMPG and choose Options ->
Environmental Settings:
In the Audio Engine tab you can point TMPG to
programs that will do parts of the conversion for you. As you can see I
have external programs for layer-2 (mp2), Layer-3 (mp3) and sample rate
changing. The one you need is the Layer-2 (mp2) audio which you should
point to the tooLAME file you have extracted like I have done.
Audio encoding settings in TMPG are fairly simple
and the minimum quality settings I think you should choose are:
Of course, make sure the sample rate is the same
as your input file. If you think that Joint Stereo loses too much of
the stereo separation for you then by all means choose normal Stereo
for better sound. As for bitrate... well larger is better but for mpeg
layer 2 audio you don't really want to be going any less than 192.
128kbps may be ok for mp3s but it's not good for mp2 audio. 224kbps is
the standard for vcd audio so that's what I recommend. If you are doing
an MPEG2 DVD master of your video then don't skimp on the audio -
choose 384kbps.
That should be all you need to know for mp2 audio
in your mpeg file.
mp3 - TMPG doesn't have a default option
for mp3 encoding, you need to use an external compressing tool. Look at
the setup above for the TooLAME mp2 encoder and you will see that I
have a LAME mp3 encoder for layer 3 audio compression. This is what you
should do for mp3 audio. The lame.exe can be found in the besweet
folder in the amvapp directory, alternatively you can get the LAME mp3 encoder files from here.
Again, the audio settings are the same as before
except now you can choose Mpeg1 Audio Layer III as your compression
type. So, again choose the correct sample rate and choose Joint Stereo
(or Stereo if you want that extra edge with the sound). For the bitrate
you should choose 128kbps or above. Personally I think 160kbps is a
good value for an acceptable quality/size ratio but if you can go
higher,
please do - if you do a 224kbps encode it will be the same size as
the layer 2 audio version but the quality will be much much better.
AbsoluteDestiny -
September 2003