mpvclip: implement 2-pass mode!

2 files changed, 97 insertions, 24 deletions

diff --git a/README.adoc b/README.adoc
index 8ff3533..d44dfc6 100644
--- a/README.adoc
+++ b/README.adoc
@@ -3,7 +3,7 @@
 
 == Scripts
 
-* *mpvclip.* Clip sections of video with ffmpeg. Allows choosing CRF/two-pass target size and preset, with sensible defaults. As of 2025-03-01, requires recent mpv git master build.
+* *mpvclip.* Clip sections of video with ffmpeg. Allows choosing CRF/two-pass target size, with sensible defaults. As of 2025-03-01, requires recent mpv git master build.
 * *get_subtitle.* Copy the text of the current subtitle line to the clipboard. Relies on `https://github.com/astrand/xclip[+xclip+`] to function.
 
 == Copying
diff --git a/mpvclip/main.lua b/mpvclip/main.lua
index 88beb30..bfbc332 100644
--- a/mpvclip/main.lua
+++ b/mpvclip/main.lua
@@ -1,11 +1,11 @@
 local input = require "mp.input"
 
-local function dump_arr(arr)
-    local result = ""
-    for _, v in ipairs(arr) do
-        result = result .. string.format("%q", v) .. ", "
+local function log_cmd(args)
+    local cmd = ""
+    for _, v in ipairs(args) do
+        cmd = cmd .. string.format("%q", v) .. ", "
     end
-    return result
+    print("Running command: " .. cmd)
 end
 
 local function extend(arr1, arr2)
@@ -14,14 +14,27 @@ local function extend(arr1, arr2)
     end
 end
 
+local function copy_arr(arr)
+    local result = {}
+    for _, v in ipairs(arr) do
+        table.insert(result, v)
+    end
+    return result
+end
+
 local function do_clip(a, b, crf, two_pass_target, sub_track_id, path)
+    local AUDIO_CODEC = "libopus"
+    local AUDIO_BITRATE_KIBIBITS = 128
+    local AUDIO_BITRATE_STR = tostring(AUDIO_BITRATE_KIBIBITS) .. "k"
+
     local filterchain = nil
     if sub_track_id then
         filterchain = string.format("subtitles='%s':si=%d", path, sub_track_id - 1)
     end
 
     local out_path = string.format("clip_%d.mp4", os.time())
-    local args = {
+
+    local base_args = {
         "ffmpeg",
         "-hide_banner",
         "-loglevel", "warning",
@@ -29,28 +42,73 @@ local function do_clip(a, b, crf, two_pass_target, sub_track_id, path)
         "-to", b,
         "-copyts",
         "-i", path,
+        "-c:v", "libx264",
         "-ss", a,
         "-to", b,
     }
     if filterchain then
-        extend(args, { "-filter_complex", filterchain })
+        extend(base_args, { "-filter_complex", filterchain })
     end
+
     if crf then
-        extend(args, { "-crf", crf })
-    end
-    extend(args, {
-        "-pix_fmt", "yuv420p",
-        "-movflags", "+faststart",
-        "-c:a", "libopus",
-        "-b:a", "128k",
-        out_path
-    })
+        local args = copy_arr(base_args)
+        extend(args, {
+            "-crf", crf,
+            "-pix_fmt", "yuv420p",
+            "-movflags", "+faststart",
+            "-c:a", AUDIO_CODEC,
+            "-b:a", AUDIO_BITRATE_STR,
+            out_path
+        })
 
-    print(dump_arr(args))
+        log_cmd(args)
+        mp.command_native({ name = "subprocess", args = args })
+    elseif two_pass_target then
+        local clip_secs = (tonumber(b) - tonumber(a))
+        local total_bytes = two_pass_target * 1024 * 1024
+        local audio_bytes = AUDIO_BITRATE_KIBIBITS * (1024 / 8) * clip_secs
+        local video_bytes = total_bytes - audio_bytes
+        local video_bitrate = video_bytes / clip_secs * 8
 
-    mp.command_native({ name = "subprocess", args = args })
-    mp.osd_message("mpvclip: wrote clip to " .. out_path)
-    print("Wrote clip to " .. out_path)
+        print(string.format("Clip audio will take up %d bytes, leaving %d for video", audio_bytes, video_bytes))
+        if video_bytes <= 0 then
+            local message = "Can't clip: not enough space for video"
+            mp.osd_message(message)
+            print(message)
+            return
+        end
+
+        local args = copy_arr(base_args)
+        extend(args, {
+            "-b:v", tostring(video_bitrate),
+            "-pass", "1",
+            "-an",
+            "-f", "null",
+            "-"
+        })
+
+        log_cmd(args)
+        mp.command_native({ name = "subprocess", args = args })
+
+        args = copy_arr(base_args)
+        extend(args, {
+            "-b:v", tostring(video_bitrate),
+            "-pass", "2",
+            "-c:a", AUDIO_CODEC,
+            "-b:a", AUDIO_BITRATE_STR,
+            out_path
+        })
+
+        log_cmd(args)
+        mp.command_native({ name = "subprocess", args = args })
+
+        os.remove("ffmpeg2pass-0.log")
+        os.remove("ffmpeg2pass-0.log.mbtree")
+    end
+
+    local message = "Wrote clip to " .. out_path
+    mp.osd_message(message)
+    print(message)
 end
 
 local function get_params()
@@ -58,7 +116,7 @@ local function get_params()
     local b = mp.get_property("ab-loop-b")
 
     if a == "no" or b == "no" then
-        mp.osd_message("mpvclip: a-b loop not set; doing nothing")
+        mp.osd_message("Can't clip: a-b loop not set; doing nothing")
         return
     end
 
@@ -66,12 +124,13 @@ local function get_params()
     local sub_track_id = mp.get_property_native("current-tracks/sub/id")
 
     input.select({
-        prompt = "mpvclip: select encoding mode",
+        prompt = "Select encoding mode",
         items = { "CRF", "2-pass" },
         default_item = 1,
         keep_open = true,
         submit = function(id)
             if id == 1 then
+                -- CRF mode
                 input.get({
                     prompt = "Choose CRF (0-51):",
                     default_text = "23",
@@ -79,7 +138,21 @@ local function get_params()
                         if tonumber(crf) then
                             do_clip(a, b, crf, nil, sub_track_id, path)
                         else
-                            mp.osd_message("mpvclip: invalid CRF; doing nothing")
+                            mp.osd_message("Invalid CRF; doing nothing")
+                        end
+                    end,
+                })
+            elseif id == 2 then
+                -- 2-pass mode
+                input.get({
+                    prompt = "Choose target output size in mebibytes:",
+                    default_text = "50",
+                    submit = function(two_pass_target)
+                        two_pass_target = tonumber(two_pass_target)
+                        if two_pass_target then
+                            do_clip(a, b, nil, two_pass_target, sub_track_id, path)
+                        else
+                            mp.osd_message("Invalid size, doing nothing")
                         end
                     end,
                 })