How to amplify the audio in a video file? [duplicate]

Possible Duplicate:
How to increase the volume for an avi file

What is the simplest way I can amplify the audio in a video file (.avi, .mpg, .flv, etc)?

I transfer these videos and watch them on a portable device (cellphone). Sometimes their audio level is so low that it is barely audible, even when the volume of the player (in the portable device) is turned to the maximum.

(I am using Windows.)

You'll need to do this in following steps.

1. Demux (extract) the audio stream from the container, depending on your container you should use the correct application. For a general purpose demuxer you could use ffmpeg. But there are more user friendly programs such as VirtualDub for avi, TMPGEnc for mpg files.
   • Decode the audio to a wave file (not always needed if Audacity can open the file directly)
   • Increase the volume of your audio track using Audacity by gaining your audio file such as described in the first step in this howto.
   • Save the result as a wave file.
   • Encode the wave file using the right tool for your desired audio coded (lame for mp3, faac for aac)
   • Remux the new audio and original video tracks back into the desired container using the same program you used for demuxing.