"mpng" writes a series of numbered movie frames to png files with
the specified prefix. If the "ray_trace_frames" variable is
non-zero, these frames will be ray-traced. This operation can take
several hours for a long movie.
Be sure to disable "cache_frames" when issuing this operation on a
long movie (>100 frames) to avoid running out of memory.
mpng prefix [, first [, last]]
Options "first" and "last" can be used to specify an inclusive
interval over which to render frames. Thus, you can write a smart
Python program that will automatically distribute rendering over a
cluster of workstations. If these options are left at zero, then
the entire movie will be rendered.
cmd.mpng( string prefix, int first=0, int last=0 )