Homebrewed Music

In my last blog entry I described the process for merging audio and video recorded on two different devices, for instance, replacing the audio in a Flip Mino HD video with audio recorded on a Zoom H2. This is a very handy technique, and can give great audio quality in the final video, but sometimes we only have camera sound available. So this post will describe the steps involved in separating the audio from the video, processing the audio, and merging the improved audio stream back to the video.

Naturally a cheapskate like me is only interested in free solutions, so the software tools for this project are Avidemux for video and Wavosaur for audio. With these two tools we can tweak our camera audio by raising volume, adding reverb, adjusting tone, and so on.

Trim Video and Extract Audio

We start by opening the video in Avidemux. Next we trim the video to eliminate alternate takes and start and stop activity that we don’t need to display. The A and B markers in Avidemux make this an easy task, just be sure to only set these markers on I frames, not P frames. Then set the container format to match the original video, and save the file, preferably to a new name, retaining the original. Avidemux will only save the portion of the video within the A and B markers. As always with Avidemux we must enter the file extension, and it should match the container format.

Next, open the newly saved trimmed file. We want to save the audio as an uncompressed WAV file in most cases, so set the Audio codec to PCM. Then save the audio from this video using the Audio : Save menu option, being sure to add the .WAV extension. Close Avidemux.

Enhance Audio with Wavosaur

Now start Wavosaur and open the newly extracted audio file. In our example we’ll only adjust the volume, and we’ll do that in the simplest way, by normalizing the file to -3dB. (Maximum volume in a digital audio file is called 0dB, so all volume levels are expressed as negative numbers.) Use the Process : Normalize menu option, then select Custom and set the value to -3. The audio file is now noticeably louder. Save the file and close Wavosaur.

Merge Enhanced Audio with Avidemux

Restart Avidemux and open the trimmed clip. Set the container Format to match the file type. Now merge the enhanced audio file using the Audio : Main Track menu option. Set the source to External WAV and Open the file we just ehanced in Wavosaour. We’re almost done, but we need to recompress the audio – it’s currently an uncompressed WAV file and we need to return it to the AAC format (or other as appropriate) that we started with. So set the Audio field to the AAC codec and save the file. Now you’re ready to upload your video with its enhanced audio.

Of course it’s a lot easier to follow these steps in a video demonstration, so please check this one out.

VST Plugins

Wavosaur is a handy audio tool with a simple interface and good performance, but it needs a little help from some other free software tools called VST plugins. These are software tools for audio that can be added to any program that knows how to be a VST host, and Wavosaour is just such a program.

Some of my favorite VST plugins are created by Kjaerhus Audio. The Classic series of effects are all free downloads, and no one should be without Classic EQ and Classic Reverb.

While I was perusing the Wavosaur tutorials I discovered another EQ tool, called PushTec 5.1 and I was startled by the excellent selection of presets. Be sure to spend a few moments going through the tutorials to better understand the power of Wavosaur and of this terrific free utility.