autosub.lua

-- requires subdl: https://github.com/akexakex/subdl
-- default keybinding: b
-- add the following to your input.conf to change the default keybinding:
-- keyname script_binding subdl_load_subs
local utils = require 'mp.utils'
local subdl = "/usr/bin/subdl" -- use 'which subdl' to find the real path

function subdl_load()
    local video_name=mp.get_property("filename"):gsub(".[^.]+$", "")
    sub_loaded=string.match(mp.get_property("track-list"), '"type":"sub"')

    local substore = os.getenv ( "HOME" ) .. "/.local/share/mpv/"
    local path_to_sub = substore .. video_name .. ".srt"
    t = {}
    local ssub_exists=io.open(path_to_sub,"r")
    local filepath=io.open(mp.get_property("path"),"r")
    if (mp.get_property("filename"):gsub("^.*[.]","") == "pls" or sub_loaded~=nil) then
	    mp.msg.warn("Subtitle loaded or playlist")
    elseif (filepath==nil and ssub_exists==nil) then
	    t.args = {subdl, "--lang=eng", "--download=first", "--search", video_name, "--output", path_to_sub, "/dev/null"}
            res = utils.subprocess(t)
	    if res.status == 0 then
		    mp.commandv("sub-add", path_to_sub)
	    else
		    mp.msg.warn("Subtitle download failed")
		    mp.osd_message("Subtitle download failed")
	  
	    end
    elseif (filepath==nil and ssub_exists~=nil) then
	    mp.commandv("sub-add", path_to_sub)
    elseif (filepath~=nil and sub_loaded==nil) then
	    mp.osd_message("Searching subtitles...")
	    t.args = {subdl, "--lang=eng", "--download=first", mp.get_property("path")}
	    res = utils.subprocess(t)
		mp.msg.warn(res.status)
	    if res.status == 0 then
        	mp.commandv("rescan_external_files", "reselect") 
	    elseif res.status == 1 then
		    mp.msg.warn("Subtitle download failed")
		    mp.osd_message("Subtitle download failed")
	   end
    else
	    print("no need for download")
    end

end
mp.register_event("file-loaded", subdl_load)
-- mp.add_key_binding("b", "subdl_load_subs", subdl_load)

autosub.lua fork that downloads subtitles for streams aside of files