Add Ability to Download and Merge Audio and Video media from Separate Sources

[adanvdo]

see case #158 Add an option to specify a second source for audio/video when downloading a single audio or video format

[adanvdo]

I think the best solution for this would be a mixer system.

1. Add an "Add to Mixer" button to the control panel. When this button is clicked, store all of the related download options and info in a "Video" or "Audio" record that is added to a Mix list
2. Create a simple Mixer interface that allows the user to set the start times and durations for the current mix list.
3. Download and process the mix

[adanvdo]

This is going to require a custom built timeline control