ytdl_hook: expose some JSON fields as tags

Shows uploader, channel, description fields. This works only if the
media media is constructed as EDL (for youtube it usually does this),
and if the all_formats option is not set to true (does anyone even use
it?). The former usually happens because youtube serves audio and video
separately, though it will not for live HLS/DASH. The latter uses
delayed media opening, which breaks the global_tags mechanism (see
previous commit).

player/lua/ytdl_hook.lua

@@ -38,6 +38,16 @@ function iif(cond, if_true, if_false)
     return if_false
 end
 
+-- youtube-dl JSON name to mpv tag name
+local tag_list = {
+    ["uploader"]        = "uploader",
+    ["channel_url"]     = "channel_url",
+    -- these titles tend to be a bit too long, so hide them on the terminal
+    -- (default --display-tags does not include this name)
+    ["description"]     = "ytdl_description",
+    -- "title" is handled by force-media-title
+}
+
 local safe_protos = Set {
     "http", "https", "ftp", "ftps",
     "rtmp", "rtmps", "rtmpe", "rtmpt", "rtmpts", "rtmpte",
@@ -341,6 +351,20 @@ local function as_integer(v, def)
     return def
 end
 
+local function tags_to_edl(json)
+    local tags = {}
+    for json_name, mp_name in pairs(tag_list) do
+        local v = json[json_name]
+        if v then
+            tags[#tags + 1] = mp_name .. "=" .. edl_escape(tostring(v))
+        end
+    end
+    if #tags == 0 then
+        return nil
+    end
+    return "!global_tags," .. table.concat(tags, ",")
+end
+
 -- Convert a format list from youtube-dl to an EDL URL, or plain URL.
 --  json: full json blob by youtube-dl
 --  formats: format list by youtube-dl
@@ -475,6 +499,11 @@ local function formats_to_edl(json, formats, use_all_formats)
     if #streams == 1 and single_url then
         res.url = single_url
     elseif #streams > 0 then
+        local tags = tags_to_edl(json)
+        if tags then
+            -- not a stream; just for the sake of concatenating the EDL string
+            streams[#streams + 1] = tags
+        end
         res.url = "edl://" .. table.concat(streams, ";")
     else
         return nil