Is it possible to boost the vol. levels in an aac file losslessly? I know I can decode it to wav, boost the levels, then re-encode it to aac, but that is clearly lossy. Is there some util that will allow me to some how do it using the existing aac file without decoding/reencoding? The file is a soundtrack to a video file so I can't use replaygain or the like; it has to actually be in the native aac file if that makes sense. (I also posted the same question in the vorbis forum not to double post, but because I have both aac and vorbis streams that need this correction).

Thanks!

AACGain ?

My understanding of xxxgain is that it writes values to the tag in the file. Again, this is the soundtrack to a video file and will be packaged in an mp4 container. I don't think mplayer can read aacgain tags... or can it?

I've only ever used MP3Gain, but for it I can say for sure that it changes the volume in a way that is independent of the player. Once you've applied the adjustment, it's working everywhere, not only in players that support ReplayGain.

Just do a test, take a loud file in the format of your choice (e.g. AAC), make a copy and process it with AACGain. Then listen to both files in a player that can't handle ReplayGain, and if you hear a difference, then you have your answer.

aacgain is like mp3gain in that it can change the physical volume.

The MP3Gain GUI can now change volume tags, but I don't know if aacgain also changes tags.

Does AAC gain also works with Apple Lossless?

I am still looking for the answer on the site but couldn't resist to post the question.

I don't think AACGain supports Apple lossless in that ALAC (Apple lossless) doesn't specify to any standards other than Apple's own. I looked on some change logs for AACGain and I saw that this issues was fixed: "Running AACGain on Apple lossless or other unsupported file format resulted in a crash with an unhandled exception."

So I guess AACGain will no longer crash when someone tries to open a ALAC file but I still don't think it will work. I think the only way to increase the volume of ALAC files is to either:
1. Use iTunes.
2. Encode the ALAC to a wav file, increase the volume of the wav file, and encode that wav back to ALAC. It is a pain as all tags are lost (unless you use iTunes to do the encoding to wav and back to ALAC) but it is a lossless method (since wav and ALAC are both lossless).

AACGain works in a manner similar to MP3Gain: both AAC and MP3 files have a "global_gain" field in the header for each frame of digitized audio. It is easy to change the level of a file by modifying the global_gain fields for all frames.

The actual level change is not done by tags. The tags that are written to the processed files record the gain change actually made to the file. This allows the level change to be undone without any data loss.

Although the Apple Lossless format is proprietary, it has been reverse engineered. Unfortunately there is no analogue to global_gain in that format. So I don't see any way to alter the level of an Apple Lossless file other than to play it back and re-record it.

Hope that helps...

Dave