Show video titles using yt-dlp

Different video URLs can be easy to confuse in the output of later(1).
Look up titles for them in $XDG_CACHE_HOME/later/title.json and add an
option, --update-titles, to populate the file automatically using yt-dlp.

The title is prefixed with a hash sign (#) in order to better separate
it visually from the URLs, as well as to allow easier copypasting of
output onto an mpv command line.

3 files changed, 104 insertions, 6 deletions

diff --git a/LICENSE b/LICENSE
index 36c1528..00b6ce6 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,6 @@
 ISC License
 
-Copyright (c) 2024 Wolfgang Müller
+Copyright (c) 2024 Wolfgang Müller, Juhani Krekelä
 
 Permission to use, copy, modify, and/or distribute this software for any
 purpose with or without fee is hereby granted, provided that the above
diff --git a/later b/later
index ef1ea55..ff7c478 100755
--- a/later
+++ b/later
@@ -1,8 +1,11 @@
 #!/usr/bin/env python3
 
+import argparse
 import datetime
+import json
 import os
-import argparse
+import re
+import sys
 
 from datetime import datetime as dt
 
@@ -12,6 +15,24 @@ if "XDG_STATE_HOME" in os.environ:
 
 watch_later_dir = os.path.join(xdg_state_home, "mpv/watch_later")
 
+xdg_cache_home = os.path.expanduser("~/.cache")
+if "XDG_CACHE_HOME" in os.environ:
+    xdg_cache_home = os.environ["XDG_CACHE_HOME"]
+
+later_cache_dir = os.path.join(xdg_cache_home, "later")
+title_map_file = os.path.join(later_cache_dir, "titles.json")
+
+
+class YTDLPLogger:
+    def debug(self, msg):
+        pass
+
+    def warning(self, msg):
+        pass
+
+    def error(self, msg):
+        print("later: yt-dlp:", msg, file=sys.stderr)
+
 
 def entries():
     def get_mtime(entry):
@@ -27,8 +48,35 @@ def entries():
 parser = argparse.ArgumentParser(
     prog="later", description="List mpv's watch_later entries"
 )
+parser.add_argument(
+    "-u",
+    "--update-titles",
+    action="store_true",
+    help="update titles of videos using yt-dlp",
+)
 args = parser.parse_args()
 
+if args.update_titles:
+    import yt_dlp
+
+    yt_dlp_opts = {
+        "logger": YTDLPLogger(),
+    }
+    ytdl = yt_dlp.YoutubeDL(yt_dlp_opts)
+
+write_title_map = args.update_titles
+
+try:
+    with open(title_map_file, "r") as handle:
+        title_map = json.load(handle)
+except FileNotFoundError:
+    title_map = {}
+except json.decoder.JSONDecodeError:
+    title_map = {}
+    write_title_map = True
+except Exception as err:
+    sys.exit(f"later: {err}")
+
 for path, basename, mtime in entries():
     with open(path, "r") as handle:
         first = handle.readline().rstrip()
@@ -40,10 +88,39 @@ for path, basename, mtime in entries():
         if name == "redirect entry":
             continue
 
+    if args.update_titles and name not in title_map:
+        if re.fullmatch(r"https?://.*", name):
+            try:
+                info = ytdl.extract_info(name, download=False)
+
+                # The generic extractor uses the filename part of the url as the
+                # title. Since we already display the URL, this adds no extra
+                # information.
+                if info["extractor"] == "generic":
+                    title_map[name] = ""
+                else:
+                    title_map[name] = info["title"]
+
+            except yt_dlp.utils.DownloadError:
+                pass
+
     def format_time(time):
         now = dt.now()
         if time < now - datetime.timedelta(days=7):
             return time.strftime("%b %d  %Y")
         return time.strftime("%b %d %H:%M")
 
-    print(f"{format_time(mtime)}\t{name}")
+    output = [format_time(mtime), name]
+
+    if title := title_map.get(name):
+        output.append("# " + title)
+
+    print(*output, sep="\t")
+
+if write_title_map:
+    try:
+        os.mkdir(later_cache_dir)
+    except FileExistsError:
+        pass
+    with open(title_map_file, "w") as handle:
+        json.dump(title_map, handle)
diff --git a/later.1 b/later.1
index 6b2bec9..c0ba5e5 100644
--- a/later.1
+++ b/later.1
@@ -1,4 +1,4 @@
-.Dd September 10, 2024
+.Dd September 12, 2024
 .Dt LATER 1
 .Os
 .Sh NAME
@@ -6,12 +6,31 @@
 .Nd list mpv's watch_later entries
 .Sh SYNOPSIS
 .Nm
-.Op Fl h
-.Op Fl \-help
+.Op Fl u | \-update-titles
+.Nm
+.Fl h | \-help
 .Sh DESCRIPTION
 .Nm
 lists all watch_later entries as saved by
 .Xr mpv 1 .
+.Pp
+The options are as follows:
+.Bl -tag -width "-h, --update-titles"
+.It Fl u , Fl \-update-titles
+update titles of videos using yt-dlp
+.It Fl h , Fl \-help
+show a conscise help message
+.El
+.Sh FILES
+.Bl -tag -width "1"
+.It Pa $XDG_CACHE_HOME/later/titles.json
+JSON-encoded mapping of URLs to video titles.
+Populated by running
+.Nm
+with the
+.Fl \-update-titles
+option.
+.El
 .Sh SEE ALSO
 .Xr mpv 1
 .Sh AUTHORS
@@ -19,3 +38,5 @@ lists all watch_later entries as saved by
 .Nm
 was written by
 .An Wolfgang Müller Aq Mt wolf@oriole.systems
+with yt-dlp integration by
+.An Juhani Krekelä Aq Mt juhani@krekelä.fi