Proper Transparency detection and faster processing

[Notenlish]

• Detect file extension. There are a couple of options:
  • It could be an image, if so check if image extension has transparency
  • It could be a GIF, assume it has transparency and use png.
  • It could be a video, if its a video do these:
    • ffprobe -v error -select_streams v:0 -show_entries stream=pix_fmt -of csv=p=0 [input_file]
    • If it has alpha data, use png
    • If it doesnt, use jpg
    • ffprobe should only be ran if the cache was not found