Properly support different encoders and extensions

Also fixes the output_template documentation, expects ${ext} in the template
and warns if it's missing.

src/main.lua

@@ -41,11 +41,13 @@ function expand_output_path(cropbox)
     local filename = mp.get_property_native("filename")
     local playback_time = mp.get_property_native("playback-time")
 
+    local filename_without_ext, extension = filename:match("^(.+)%.(.-)$")
+
     local properties = {
       path = mp.get_property_native("path"), -- Original path
 
-      filename = filename:match("^(.+)%..+$"), -- Filename without extension
-      file_ext = filename:gsub("^(.+)%..+$", ""), -- Original extension with leading dot
+      filename = filename_without_ext, -- Filename without extension
+      file_ext = extension or "",            -- Original extension without leading dot
 
       pos = mp.get_property_native("playback-time"),
 
@@ -60,7 +62,7 @@ function expand_output_path(cropbox)
 
       unique = 0,
 
-      ext = option_values.output_format
+      ext = option_values.output_extension
     }
     local propex = PropertyExpander(MPVPropertySource(properties))
 
@@ -159,7 +161,8 @@ function screenshot(crop)
     args = {
     "mpv", input_path,
     "--vf=crop=" .. crop_string,
-    "--frames=1", "--ovc=png",
+    "--frames=1",
+    "--ovc=" .. option_values.output_format,
     "-o", output_path
     }
   }
@@ -186,6 +189,34 @@ end
 -- Instances, binds --
 ----------------------
 
+-- Sanity-check output_template
+if option_values.warn_about_template and not option_values.output_template:find('%${ext}') then
+  msg.warn("Output template missing ${ext}! If this is desired, set warn_about_template=yes in config!")
+end
+
+-- Short list of extensions for encoders
+local ENCODER_EXTENSION_MAP = {
+  png      = "png",
+  mjpeg    = "jpg",
+  targa    = "tga",
+  tiff     = "tiff",
+  gif      = "gif", -- please don't
+  bmp      = "bmp",
+  jpegls   = "jpg",
+  ljpeg    = "jpg",
+  jpeg2000 = "jp2",
+}
+-- Pick an extension if one was not provided
+if option_values.output_extension == "" then
+  local extension = ENCODER_EXTENSION_MAP[option_values.output_format]
+  if not extension then
+    msg.error("Unrecognized output format '" .. option_values.output_format .. "', unable to pick an extension! Bailing!")
+    mp.osd_message("mpv_crop_script was unable to choose an extension, check your config", 3)
+  end
+  option_values.output_extension = extension
+end
+
+
 display_state = DisplayState()
 asscropper = ASSCropper(display_state)
 asscropper.overlay_transparency = option_values.overlay_transparency

src/options.lua

@@ -13,10 +13,28 @@ local option_values = script_options.values
 script_options:add_options({
   {nil, nil, "mpv_crop_script.lua options and default values"},
   {nil, nil, "Output options #", true},
-  {"output_template", "${filename} ${#pos:%02h.%02m.%06.3s} ${!full:${crop_w}x${crop_h} ${%unique:%03d}}.png",
-    "Directory to save (temporary) encode scripts in. Same default as with output_directory"},
+  {"output_template", "${filename} ${#pos:%02h.%02m.%06.3s} ${!full:${crop_w}x${crop_h} ${%unique:%03d}}.${ext}",
+    "Filename output template. See README.md for property expansion documentation."},
+  {nil, nil, [[Script-provided properties:
+  filename    - filename without extension
+  file_ext    - original extension without leading dot
+  path        - original file path
+  pos         - playback time
+  ext         - output file extension without leading dot
+  crop_w      - crop width
+  crop_h      - crop height
+  crop_x      - left
+  crop_y      - top
+  crop_x2     - right
+  crop_y2     - bottom
+  full        - boolean denoting a full (temporary) screenshot instead of crop
+  unique      - counter that will increase per each existing filename, until a unique name is found]]},
+
   {"output_format", "png",
-    "Format (encoder) to save final crops in"},
+    "Format (encoder) to save final crops in. For example, png, mjpeg, targa, bmp"},
+  {"output_extension", "",
+    "Output extension. Leave blank to try to choose from the encoder (if supported)"},
+
   {"create_directories", false,
     "Whether to create the directories in the final output path (defined by output_template)"},
   {"skip_screenshot_for_images", true,
@@ -39,6 +57,8 @@ script_options:add_options({
     "Try to check if video is light or dark upon opening crop tool, and invert the colors if necessary"},
 
   {nil, nil, "Misc options #", true},
+  {"warn_about_template", true,
+    "Warn about output_template missing ${ext}, to ensure the extension is not missing"},
   {"disable_keybind", false,
     "Disable the built-in keybind"}
 })