These scripts will be called to perform URL Translation or text playlist parsing.
A large volume of info on these scripts can already be found here (some info here is taken from this resource).

Playlist Parser VLC Fields

• vlc.path URL string (without the leading http:// or file:// element)
• vlc.access Access used (“http” for http://, “file” for file://, etc.)

Playlist Paraser VLC Functions

These are methods in the global vlc object that are available to playlist parsers.

vlc.read()

Read data from a playlist file.
NOTE: Cannot be used in probe().

Parameters

• numchars Number of characters to read from the playlist file

Return value

Characters read from the playlist file

vlc.readline()

Like vlc.read, but only one line.
NOTE: Cannot be used in probe().

Return value

Characters read from the playlist file line

vlc.peek()

Like vlc.read(), but the first numchars characters are read from the playlist file.

Parameters

• numchars Number of characters to read from the start of the playlist file

Return value

Characters read from the playlist file

Special Functions

These are functions that VLC expects in playlist parsers and are required in order for them to run properly.

probe()

This function tells VLC if the Lua script should be used (function returns true) or not (function returns false) given a specific URL, read via vlc.access.

Example

function probe()
  if vlc.access ~= "http"
  then
		return false
  end
  if string.match( vlc.path, "video.google.com/videoplay" )
  then
		return true
  else
		return false
  end
end

Return value

This function should only return a boolean

parse()

If the probe() function returns true, VLC will use the parse() to ask for the new playlist item(s) which need to be added.
Data is passed to the parser from VLC via the vlc.read() and vlc.readline() functions and other VLC object fields.

Example

function parse()
  item = {}
  item.path = "http://" .. string.gsub( vlc.path, "videoplay", "videogvp" )
  item.name = "Some Google video playlist"
  return { item }
end

Return value

This function should return a table representing a new playlist item; these items should use the same format as playlist.add().

Examples

Here is a simple example of a playlist parser script authored by Pierre Ynard of the VideoLAN team, which handles Vocaroo links.

-- Probe function.
function probe()
	return ( vlc.access == "http" or vlc.access == "https" )
		and string.match( vlc.path, "^vocaroo%.com/." )
end

-- Parse function.
function parse()
   -- The HTML page contains no metadata and is not worth parsing
   local id = string.match( vlc.path, "^vocaroo%.com/([^?]+)" )

   -- Dispatch media to correct CDN server
   local cdn = ( string.len( id ) == 10 or
					( string.len( id ) == 12 and string.match( id, "^1" ) ) )
			and "//media1.vocaroo.com/mp3/"
			or "//media.vocaroo.com/mp3/"

	local path = vlc.access..":"..cdn..id
	return { { path = path } }
end