adding video compression (h264)

[bsobhani]

Starting pull request for video compression (h264) support. Not close to being perfect, but getting the process started so that it does not linger.

Basic functionality works and seems stable on the machines I tested it on. Achieves lower compression sizes with higher quality than existing codecs for some types of image sequences. For example, if the differences between frames is consistently small, like at SNS beamlines where neutron events accumulate on an image.

To compile, set:

WITH_VC=YES VC_EXTERNAL=NO

To use, select "H264" from $(P)$(R)Compressor.

Tuning PVs:

• $(P)$(R)QMinMax - 1 for least lossless compression, higher values for lossier compression
• $(P)$(R)GOPSize - Group of picture size. 1 for frame-by-frame compression. Set to higher values for true video compression.

[bsobhani]

Erico, thank you for the feedback. I have responded to some of your comments. When I have time I will take a more thorough look at the pull request and probably make some additional commits.