Use multiple workers instead of a single server

Simply copy the _server.lua once or twice in the
scripts directory. They will register themselves with
the "client" automatically. Props to anon for reminding me.

This improves performance a bunch, at the cost of,
well, peformance. Your CPU will max out.

It'd be cool to automatically generate the workers
from the main script, but you can't tell mpv to load
up a script, as far as I know.

Author: TheAMM

cat_server.json

@@ -5,7 +5,6 @@
 		"<version>",
 		"lib/helpers.lua",
 		"src/options.lua",
-		"src/thumbnailer_shared.lua",
 		"src/thumbnailer_server.lua"
 	],
 

src/thumbnailer_server.lua

@@ -82,35 +82,17 @@ function check_output(ret, output_path)
 end
 
 
-function generate_thumbnails(from_keypress)
-    msg.debug("Thumbnailer state:")
-    msg.debug(utils.to_string(Thumbnailer.state))
-
-    if not Thumbnailer.state.available then
-        if from_keypress then
-            mp.osd_message("Nothing to thumbnail", 2)
-        end
-        if Thumbnailer.state.is_remote then
-            msg.warn("Not thumbnailing remote file")
-        end
+function do_worker_job(state_json_string, frames_json_string)
+    local thumb_state, err = utils.parse_json(state_json_string)
+    if err then
+        msg.error("Failed to parse state JSON")
         return
     end
 
-    local thumbnail_count = Thumbnailer.state.thumbnail_count
-    local thumbnail_delta = Thumbnailer.state.thumbnail_delta
-    local thumbnail_size = Thumbnailer.state.thumbnail_size
-    local file_template = Thumbnailer.state.thumbnail_template
-    local file_duration = mp.get_property_native("duration")
-    local file_path = mp.get_property_native("path")
-
-    msg.info(("Generating %d thumbnails @ %dx%d"):format(thumbnail_count, thumbnail_size.w, thumbnail_size.h))
-
-    -- Create directory for the thumbnails
-    local thumbnail_directory = split_path(file_template)
-    local l, err = utils.readdir(thumbnail_directory)
+    local thumbnail_indexes, err = utils.parse_json(frames_json_string)
     if err then
-        msg.info("Creating", thumbnail_directory)
-        create_directories(thumbnail_directory)
+        msg.error("Failed to parse thumbnail frame indexes")
+        return
     end
 
     local thumbnail_func = create_thumbnail_mpv
@@ -122,7 +104,10 @@ function generate_thumbnails(from_keypress)
         end
     end
 
-    if Thumbnailer.state.is_remote then
+    local file_duration = mp.get_property_native("duration")
+    local file_path = mp.get_property_native("path")
+
+    if thumb_state.is_remote then
         thumbnail_func = create_thumbnail_mpv
         if thumbnailer_options.remote_direct_stream then
             -- Use the direct stream (possibly) provided by ytdl
@@ -132,14 +117,16 @@ function generate_thumbnails(from_keypress)
         end
     end
 
-    mp.commandv("script-message", "mpv_thumbnail_script-enabled")
+    msg.debug(("Generating %d thumbnails @ %dx%d"):format(#thumbnail_indexes, thumb_state.thumbnail_size.w, thumb_state.thumbnail_size.h))
 
     local generate_thumbnail_for_index = function(thumbnail_index)
+        local thumbnail_path = thumb_state.thumbnail_template:format(thumbnail_index)
+        local timestamp = math.min(file_duration, thumbnail_index * thumb_state.thumbnail_delta)
 
         mp.commandv("script-message", "mpv_thumbnail_script-progress", tostring(thumbnail_index))
 
         -- The expected size (raw BGRA image)
-        local thumbnail_raw_size = (thumbnail_size.w * thumbnail_size.h * 4)
+        local thumbnail_raw_size = (thumb_state.thumbnail_size.w * thumb_state.thumbnail_size.h * 4)
 
         local need_thumbnail_generation = false
 
@@ -158,7 +145,7 @@ function generate_thumbnails(from_keypress)
         end
 
         if need_thumbnail_generation then
-            local ret = thumbnail_func(file_path, timestamp, thumbnail_size, thumbnail_path)
+            local ret = thumbnail_func(file_path, timestamp, thumb_state.thumbnail_size, thumbnail_path)
             local success = check_output(ret, thumbnail_path)
 
             if success == nil then
@@ -200,33 +187,35 @@ function generate_thumbnails(from_keypress)
         mp.commandv("script-message", "mpv_thumbnail_script-ready", tostring(thumbnail_index), thumbnail_path)
     end
 
-    -- Keep track of which thumbnails we've checked during the passes (instead of proper math for no-overlap)
-    local generated_thumbnails = {}
-
-    -- Do several passes over the thumbnails with increasing frequency
-    for res = 6, 0, -1 do
-        local nth = (2^res)
-
-        for thumbnail_index = 0, thumbnail_count-1, nth do
-            if not generated_thumbnails[thumbnail_index] then
-                local bail = generate_thumbnail_for_index(thumbnail_index)
-                if bail then return end
-                generated_thumbnails[thumbnail_index] = true
-            end
-        end
+    for i, thumbnail_index in ipairs(thumbnail_indexes) do
+        local bail = generate_thumbnail_for_index(thumbnail_index)
+        if bail then return end
     end
 end
 
+-- Set up listeners and keybinds
 
-function on_script_keypress()
-    mp.osd_message("Starting thumbnail generation", 2)
-    generate_thumbnails(true)
-    mp.osd_message("All thumbnails generated", 2)
-end
+-- Job listener
+mp.register_script_message("mpv_thumbnail_script-job", do_worker_job)
 
--- Set up listeners and keybinds
 
-mp.register_script_message("mpv_thumbnail_script-generate", generate_thumbnails)
+-- Register this worker with the master script
+local register_timer = nil
+local register_timeout = mp.get_time() + 3
+
+local register_function = function()
+    if mp.get_time() > register_timeout and register_timer then
+        msg.error("Thumbnail worker registering timed out")
+        register_timer:stop()
+    else
+        msg.debug("Announcing self to master...")
+        mp.commandv("script-message", "mpv_thumbnail_script-worker", mp.get_script_name())
+    end
+end
+
+register_timer = mp.add_periodic_timer(0.1, register_function)
 
-local thumb_script_key = not thumbnailer_options.disable_keybinds and "T" or nil
-mp.add_key_binding(thumb_script_key, "generate-thumbnails", on_script_keypress)
+mp.register_script_message("mpv_thumbnail_script-slaved", function()
+    msg.debug("Successfully registered with master")
+    register_timer:stop()
+end)

src/thumbnailer_shared.lua

@@ -15,7 +15,8 @@ local Thumbnailer = {
 
         finished_thumbnails = 0,
         thumbnails = {}
-    }
+    },
+    workers = {}
 }
 
 function Thumbnailer:clear_state()
@@ -197,27 +198,105 @@ function Thumbnailer:get_thumbnail_path(time_position)
 end
 
 function Thumbnailer:register_client()
-    -- Wait for server to tell us we're live
-    mp.register_script_message("mpv_thumbnail_script-enabled", function() self.state.enabled = true end)
     mp.register_script_message("mpv_thumbnail_script-ready", function(index, path)
         self:on_thumb_ready(tonumber(index), path)
     end)
     mp.register_script_message("mpv_thumbnail_script-progress", function(index, path)
         self:on_thumb_progress(tonumber(index), path)
     end)
 
-    -- Notify server to generate thumbnails when video loads/changes
+    mp.register_script_message("mpv_thumbnail_script-worker", function(worker_name)
+        if not self.workers[worker_name] then
+            msg.debug("Registered worker", worker_name)
+            self.workers[worker_name] = true
+            mp.commandv("script-message-to", worker_name, "mpv_thumbnail_script-slaved")
+        end
+    end)
+
+    -- Notify workers to generate thumbnails when video loads/changes
+    -- This will be executed after the on_video_change (because it's registered after it)
     mp.observe_property("video-dec-params", "native", function()
         local duration = mp.get_property_native("duration")
         local max_duration = thumbnailer_options.autogenerate_max_duration
 
-        if duration and thumbnailer_options.autogenerate then
+        if self.state.available and thumbnailer_options.autogenerate then
             -- Notify if autogenerate is on and video is not too long
             if duration < max_duration or max_duration == 0 then
-                mp.commandv("script-message", "mpv_thumbnail_script-generate")
+                self:start_worker_jobs()
             end
         end
     end)
+
+    local thumb_script_key = not thumbnailer_options.disable_keybinds and "T" or nil
+    mp.add_key_binding(thumb_script_key, "generate-thumbnails", function()
+        if self.state.available then
+            self:start_worker_jobs()
+            mp.osd_message("Started thumbnailer jobs")
+        else
+            mp.osd_message("Thumbnailing unavailabe")
+        end
+    end)
+end
+
+function Thumbnailer:_create_thumbnail_job_order()
+    local used_frames = {}
+    local work_frames = {}
+
+    for x = 6, 0, -1 do
+        local nth = (2^x)
+
+        for thi = 0, self.state.thumbnail_count-1, nth do
+            if not used_frames[thi] then
+                table.insert(work_frames, thi)
+                used_frames[thi] = true
+            end
+        end
+    end
+    return work_frames
+end
+
+function Thumbnailer:start_worker_jobs()
+    self.state.enabled = true
+
+    -- Create directory for the thumbnails, if needed
+    local thumbnail_directory = split_path(self.state.thumbnail_template)
+    local l, err = utils.readdir(thumbnail_directory)
+    if err then
+        msg.info("Creating", thumbnail_directory)
+        create_directories(thumbnail_directory)
+    end
+
+    local worker_list = {}
+    for worker_name in pairs(self.workers) do table.insert(worker_list, worker_name) end
+
+    local worker_count = #worker_list
+
+    if worker_count == 0 then
+        local err = "No thumbnail workers found. Make sure you are not missing a script!"
+        msg.error(err)
+        mp.osd_message(err, 3)
+
+    else
+        local frame_job_order = self:_create_thumbnail_job_order()
+        local worker_jobs = {}
+        for i = 1, worker_count do worker_jobs[worker_list[i]] = {} end
+
+        -- Split frames amongs the workers
+        for i, thumbnail_index in ipairs(frame_job_order) do
+            local worker_id = worker_list[ ((i-1) % worker_count) + 1 ]
+            table.insert(worker_jobs[worker_id], thumbnail_index)
+        end
+
+        local state_json_string = utils.format_json(self.state)
+
+        for worker_name, worker_frames in pairs(worker_jobs) do
+            if #worker_frames > 0 then
+                local frames_json_string = utils.format_json(worker_frames)
+                msg.debug("Giving job to", worker_name, frames_json_string)
+                mp.commandv("script-message-to", worker_name, "mpv_thumbnail_script-job", state_json_string, frames_json_string)
+            end
+        end
+    end
 end
 
 mp.observe_property("video-dec-params", "native", function(name, params) Thumbnailer:on_video_change(params) end)