Add an image sequence export option

[GoogleCodeExporter]

This was something I was interested in getting to work for a while now:  A 
method for exporting an image sequence that can be imported into video editing 
software such as VirtualDub in order to make a flawless, lag-free video of the 
chart as it would play back in EOF.  This would have better results than using 
screen capture software, because that software would cause EOF or the computer 
to lag during chart playback, but the image sequence method would generate the 
frames without a need to do so in real time, so processor usage peaks will not 
cause any frames to be skipped.

Original issue reported on code.google.com by raynebc on 4 Jan 2011 at 7:36

[GoogleCodeExporter]

r660 begins this enhancement by writing the logic to create the image sequence. 
 I originally tried to use eof_read_pcm_samples(), but it didn't seem to work 
right, as the ov_read function would return an error.  So I resorted to 
manually looping through and writing frames at a rate of 30fps by continually 
rendering based on the current time position and then incrementing that time.  
This probably turns out to be more efficient in the long run.

I also couldn't get Allegro to output a working TGA file, so I went with PCX 
for now.  It might be possible to try to use JPEG or PNG, although which image 
formats are supported for image sequence import depends on the video editing 
software being used.

The following are tasks to complete for this enhancement:
1. Create a dialog menu with options, such as which image format to output to, 
which parts of the window to render, or perhaps even doing one instrument track 
per quarter screen, making a multi-instrument image sequence.  Allegro's 
save_bitmap() function supposedly will export based on the extension of the 
output filename, reportedly supporting BMP, PCX and TGA.
2. Update the image sequence export routine to support the above task's options
3. Consider writing an AVI Synth format script to make it easier to encode the 
video with software such as VirtualDub.
4. Update the documentation and include a short tutorial for creating a video 
with this method.

Original comment by raynebc on 4 Jan 2011 at 8:05

[GoogleCodeExporter]

5.  Add the option to just export one screen at a time, to create one large 
concatenation representing the whole chart.  Logic may need to be added to 
ensure partially off-screen items aren't just skipped from rendering.

Original comment by raynebc on 18 May 2012 at 6:52