WAVcc WAVE channel changer

This small command line utility does one job: It changes the channelindex of a mono WAV file.

Download

http://www.belle-nuit.com/download/wavcc.dmg (4 MB)

Configuration

Macintosh G4, G5 or Intel

MacOS 10.4 or newer

Knowledge of the Terminal application and the use of command line programs

Installation

Copy the WAVcc folder from the disk to wherever you want. Do not change the name of the folder nor the content:

The WAVcc utility binary
The folder lib containing the rbframework.dylib which is needed by the utility

Open the Terminal application and cd to the parent folder of the WAVcc folder. Then call the utility WAVcc/WAVcc and you get the usage print

WAVECchannelchanger
(c) Matthias Buercher 2009 matti@belle-nuit.com
Usage
WAVcc -o n -n n filepath
WAVcc -p n folderpath
-o old channel number 1-9
-n new channel number 1-9
-p channel offset plus channel
filepath absolute shell path
folderpath absolute shell path

License

This program is freeware.

Reference

In film postproduction, the image is often recorded seperately from the sound. In the editing, a common sync mark is used to get the two tracks together. In Switzerland for example, the sound engineer records his sound to disk and uses an internal timecode generator. This timecode is send via air to the video camera to be recorded on sound track A2, while A1 records the camera mic as security.

In the Avid, the video is captured from tape with all the tracks VA1A2. The Avid reads the tomecode from A2 and puts it into Auxiliary TC1. The audio tracks in my case are imported from multiple mono WAV files. Here the Start TC is copied straight in the bin to Auxiliary TC1.

Then we select the clips and apply AutoSync and the magic creates a new clip in sync.

This works quite well, but there is a little beauty problem. If I do not remove the A1A2 track from the video clip before the sync, I get a group clip. I can select then to have the audio from either the video clip or from the sound clips, but not both.

This has to do how Avid works when creating the clip. On grouping, Avid respects the channel number and when it encounters more than one clip of the same channel, it has to create a group clip, because this is the only way to have a channel more than once in the same clip. Avid has done a great deal in the last version to come here, because early versions of AutoSync simply refused to work when there were duplicate channels.

In fiction, this is not a problem, but in documentary, you might sometimes want to know what the camera mic has done and the group clip access is cumbersome, so i prefer 5 tracks instead of 3 tracks and 3 hidden tracks (supposinng audio had 3 tracks).

The next step to think was to say lets modify the tracks of the clip, but Avid does not let you do that unless unlinking it, and this is from the workflow probably a good idea.

So we need to change the files before we import them. This is where WAVcc comes in. It changes the channel informations on several locations of the file.

In the WAVEbext chunk: If there is a sTRK(oldchannel) key, it replaces it with a sTRK(newchannel) key
In the iXML chunk: the CHANNEL_INDEX tag value changes
Apparently, Avid looks also on the filename: So "_(oldchannel).WAV" is changed to Auxiliary TC1. To not overwrite another file, a "c" is added at the beginning of the file

All these changes happen in the header part of the file and are harmless, but i suggest you not to work on originals without having backup copies.

The utility has to working modes:

You can change files one by one: WAVcc -o n -n n filepath You set the old and the new channel and the filepath which must be an absolute shellpath. Note you need to know the old channel

You can change all files in a folder WAVcc -p n folderpath where you can add a number. For example, if you want to keep both audio with the video, you just shift the audio tracks by two WAVcc -p 2 folderpath and channel 1 becomes channel 3, channel 2 becomes channel 4 etc.

Both are very fast as they change just a few bytes in each file

Limitations

This is a afternoon hackware to solve a specific problem. So there are some limitations.

You cannot go over channel 9 because the program does not deal with the fact when the length of the chunks in the header does change
On the same side there is a bug because it does change the number in the CURRENT_FILENAME tag in the iXML chunk, but not add the "c" at the beginning which would change the length of the filename
It does only deal with mono WAVE files.
It works only on Mac and only on command line, but thats not really a limitation, isn't it?

History

16.6.2009 v1.0.0

http://www.belle-nuit.com - 16.6.2009