[MPlayer-dev-eng] mencoder frame skip behavior broken

[D Richard Felker III]

I've been working on a filter for true inverse telecine, and it's
working great with mplayer, but mencoder seems a bit brain damaged...
When it needs to skip a frame to meet the desired output fps, it
passes the drop option to decode_video, like mplayer -framedrop does.
Unfortunately, this totally breaks any filters that use temporal
information to work -- pp=tn, denoise3d, and now my de-telecine
filter.

IMO, the correct solution is the make mencoder always pass 0 to
decode_video for the drop flag, and instead set a flag in the muxer
struct indicating that the frame needs to be dropped. Then the ve_*
modules are responsible for skipping encoding if the drop flag is set.
I've patched ve_lavc to do this already and it seems to work great. If
no one strongly objects, I'll do this to the other encoders too and
commit soon.

Rich