I want to convert the audio track of a MKV file to HE-AAC (AAC+/AACplus). The audio track is AC3. But there seems no GUI for HE-AAC encoding? I only found out there is a Command Line Tool (CLI) from Nero, but I don't know if this can do HE-AAC.
Any help? Any recommendation for a GUI that can convert AC3 to HE-AAC? Also should be able to handle surround sound (5.1/6-channels).
Best Answer
Nero AAC Encoder usage
neroAacEnc does support HE-AAC and HE-AAC v2 via
-he
and-hev2
parameters.This encoder is (still?) considered to be the best encoder quality wise. Nero offers it free of charge but doesn't give support for it. One problem you will encounter with large files like 5.1 WAV is the file size limitation. It is not due to this encoder being crippleware, but how to handle large numbers in a program. To workaround this you need to pipe the input with another program to the encoder and use the
-ignorelength
parameter. If you input format is already WAV the following should work:You can also use
avconv
(formerly known asffmpeg
, now forked and with the CLI tool being renamed) to do the conversion to WAV.Note that the resulting file is a MP4 with a AAC stream in a MP4 container, not a raw AAC stream. You can extract the raw stream with
MP4Box
from thegpac
package if you want to.Nero AAC quality setting
The quality setting depends on the profile you use. With LC-AAC you can go up to
-q 1.0
. HE-ACC is limited to-q 0.5
, I think, and HE-AAC v2 even lower. This is due the techniques behind those profiles that are centered around low bitrates. Using-q 0.5
will result in a file larger than common AC3 6ch audio from a DVD, using-q 0.3
will cut the file size in half.Advice for codec and quality choice on multichannel audio
The situation is (still?) really messy, which is why there exist no easy to use GUI like Handbrake. The most efficient codec is HE-AAC v2 but it is not well supported in Ubuntu, due to licensing/patent issues in some countries. Vorbis is good too, but less efficient. Multichannel mapping should be fixed in the latest LTS release (12.04, it wasn't in 10.04). Leaving out MP3, AC3 comes in third place. FLAC is 4th on efficiency and the most supported lossless format. DTS is a complete looser and should be also left out, like MP3. Convert to FLAC if you can.
So if you have AC3 encoded audio, you probably leave it at that if the device and container format supports it. The chart for supported media formats on Android might be helpful.
Appendix: neroAacEnc help file