basic support for PNG and ProRes 4444 overlay

[mediafeliz]

PNG sequence overlays

• frame_000001.png, frame_000002.png…

./bin/exc \
  -f "./media/bbb_30s.mp4" \
  -xc-type video \
  -format mp4 \
  -wm-xloc 0 \
  -wm-yloc 0 \
  -wm-sequence-path "./media/overlay_frames/frame_%06d.png"

ProRes 4444 MOV overlays with alpha

./bin/exc \
  -f "./media/bbb_30s.mp4" \
  -xc-type video \
  -format mp4 \
  -wm-xloc 0 \
  -wm-yloc 0 \
  -wm-overlay-mov "./media/overlay_prores.mov"