Rework Export window

[Andy Finch]

Some enhancements to the export window are needed. This bug report consolidates a number of others into one.

1. Don't allow invalid format/codec combinations. In the advanced tab, users can select any format/codec combination. If they are an invalid combination, it results in a crash in ffmpeg. Hanspb has created a sheet of valid combinations. See http://openshotusers.com/forum/viewtopic.php?f=27&t=1150#p5870

2. Ensure formats get exported with the commonly used extensions, i.e.mkv instead of matroska. See the sheet above for format/extension details.

3. Provide a way to export only part of the timeline, whether it is by markers on the timeline or a position counter on the export window.

4. Include the ability to save custom export settings as a new preset.

5. For advanced users, allow the use of ffmpeg encoding options directly.

6. Show encoding time estimation.

There is a thread in the forum including some good mockups.

http://openshotusers.com/forum/viewtopic.php?f=27&t=1150

[Rick Gabriel (klaxian1)]

I really like the mockups in the referenced thread and I hope these settings changes can be implemented relatively quickly. I would prefer a "Constant Quality" or similar option in the "compression method" pulldown instead of requiring users to know advanced ffmpeg encoding options. A constant quality setting is already available in Pitivi, Avidemux, Handbrake, and others for examples. There's not much left in my wishlist, but "Constant Quality" encoding is at the top. Thanks for the great work on a top notch video editor!

[Kris Thomsen (lakristho)]

Wouldn't it be easier to keep track of these bugs, if each bug/enhancement has their own bug id?

[Dan Dascalescu (ddascalescu+launchpad)]

Yes, this bug should be split into multiple tickets. One issue per bug.