stats.lua: add graphs for readahead time and total byte usage

The readahead time should be interesting for latency vs. underruns
(which idiot protocols like HLS suffer from).

The total byte usage is less interesting than I hoped; maybe the
frequency at which it samples should be reduced. (Kind of dumb - you
want high frequency for the readahead field, but much lower for byte
usage.)

Of course, the code was copy&pasted from the DS ratio/jitter stuff. Some
of the choices may not make any sense for the new code.

player/lua/stats.lua

@@ -83,6 +83,8 @@ local min = math.min
 local recorder = nil
 -- Timer used for redrawing (toggling) and clearing the screen (oneshot)
 local display_timer = nil
+-- Timer used to update cache stats.
+local cache_recorder_timer = nil
 -- Current page and <page key>:<page function> mappings
 local curr_page = o.key_page_1
 local pages = {}
@@ -92,10 +94,12 @@ local ass_stop = mp.get_property_osd("osd-ass-cc/1")
 -- Ring buffers for the values used to construct a graph.
 -- .pos denotes the current position, .len the buffer length
 -- .max is the max value in the corresponding buffer
-local vsratio_buf, vsjitter_buf
+local vsratio_buf, vsjitter_buf, cache_ahead_buf, cache_total_buf
 local function init_buffers()
     vsratio_buf = {0, pos = 1, len = 50, max = 0}
     vsjitter_buf = {0, pos = 1, len = 50, max = 0}
+    cache_ahead_buf = {0, pos = 1, len = 50, max = 0}
+    cache_total_buf = {0, pos = 1, len = 50, max = 0}
 end
 -- Save all properties known to this version of mpv
 local property_list = {}
@@ -615,9 +619,24 @@ local function cache_stats()
         return table.concat(stats)
     end
 
-    append(stats, opt_time(info["reader-pts"]) .. " - " ..
-                  opt_time(info["cache-end"]),
-           {prefix = "Packet queue:"})
+    local a = info["reader-pts"]
+    local b = info["cache-end"]
+
+    append(stats, opt_time(a) .. " - " .. opt_time(b), {prefix = "Packet queue:"})
+
+    local r = nil
+    if (a ~= nil) and (b ~= nil) then
+        r = b - a
+    end
+
+    local r_graph = nil
+    if not display_timer.oneshot and o.use_ass then
+        r_graph = generate_graph(cache_ahead_buf, cache_ahead_buf.pos,
+                                 cache_ahead_buf.len, cache_ahead_buf.max,
+                                 nil, 0.8, 1)
+        r_graph = o.prefix_sep .. r_graph
+    end
+    append(stats, opt_time(r), {prefix = "Read-ahead:", suffix = r_graph})
 
     -- These states are not necessarily exclusive. They're about potentially
     -- separate mechanisms, whose states may be decoupled.
@@ -634,8 +653,15 @@ local function cache_stats()
     end
     append(stats, state, {prefix = "State:"})
 
+    local total_graph = nil
+    if not display_timer.oneshot and o.use_ass then
+        total_graph = generate_graph(cache_total_buf, cache_total_buf.pos,
+                                     cache_total_buf.len, cache_total_buf.max,
+                                     nil, 0.8, 1)
+        total_graph = o.prefix_sep .. total_graph
+    end
     append(stats, utils.format_bytes_humanized(info["total-bytes"]),
-           {prefix = "Total RAM:"})
+           {prefix = "Total RAM:", suffix = total_graph})
     append(stats, utils.format_bytes_humanized(info["fw-bytes"]),
            {prefix = "Forward RAM:"})
 
@@ -666,6 +692,31 @@ local function cache_stats()
     return table.concat(stats)
 end
 
+local function graph_add_value(graph, value)
+    graph.pos = (graph.pos % graph.len) + 1
+    graph[graph.pos] = value
+    graph.max = max(graph.max, value)
+end
+
+-- Record 1 sample of cache statistics.
+-- (Unlike record_data(), this does not return a function, but runs directly.)
+local function record_cache_stats()
+    local info = mp.get_property_native("demuxer-cache-state")
+    if info == nil then
+        return
+    end
+
+    local a = info["reader-pts"]
+    local b = info["cache-end"]
+    if (a ~= nil) and (b ~= nil) then
+        graph_add_value(cache_ahead_buf, b - a)
+    end
+
+    graph_add_value(cache_total_buf, info["total-bytes"])
+end
+
+cache_recorder_timer = mp.add_periodic_timer(0.25, record_cache_stats)
+cache_recorder_timer:kill()
 
 -- Current page and <page key>:<page function> mapping
 curr_page = o.key_page_1
@@ -709,7 +760,6 @@ local function record_data(skip)
     end
 end
 
-
 -- Call the function for `page` and print it to OSD
 local function print_page(page)
     if o.persistent_overlay then
@@ -759,6 +809,7 @@ local function process_key_binding(oneshot)
         -- Previous and current keys were toggling -> end toggling
         elseif not display_timer.oneshot and not oneshot then
             display_timer:kill()
+            cache_recorder_timer:stop()
             clear_screen()
             remove_page_bindings()
             if recorder then
@@ -771,6 +822,7 @@ local function process_key_binding(oneshot)
         if not oneshot and (o.plot_vsync_jitter or o.plot_vsync_ratio) then
             recorder = record_data(o.skip_frames)
             mp.register_event("tick", recorder)
+            cache_recorder_timer:resume()
         end
         display_timer:kill()
         display_timer.oneshot = oneshot