fix: allow multiple values for tag "musicbrainz-artistid" & "musicbrainz-albumartistid"

issue #2

src/main.rs

@@ -1,4 +1,5 @@
 mod config;
+mod tag;
 mod ui;
 
 use crate::config::{Config, Transcode};
@@ -171,6 +172,9 @@ async fn main() -> Result<()> {
 async fn main_loop(ui_queue: ui::MsgQueue) -> Result<()> {
 	let (config, conv_args) = task::spawn_blocking(|| -> Result<_> {
 		gstreamer::init()?;
+		gstreamer::tags::register::<tag::MbArtistId>();
+		gstreamer::tags::register::<tag::MbAlbumArtistId>();
+
 		let config = config::config().context("Could not get the config")?;
 
 		let conv_args = get_conversion_args(&config)

src/tag.rs

@@ -0,0 +1,45 @@
+use glib::Value;
+use gstreamer::{
+	tags::{merge_strings_with_comma, CustomTag},
+	Tag, TagFlag,
+};
+
+pub struct MbArtistId;
+
+impl<'a> Tag<'a> for MbArtistId {
+	type TagType = &'a str;
+
+	fn tag_name<'b>() -> &'b str {
+		"musicbrainz-artistid"
+	}
+}
+
+impl CustomTag<'_> for MbArtistId {
+	const FLAG: TagFlag = TagFlag::Meta;
+	const NICK: &'static str = "artist ID";
+	const DESCRIPTION: &'static str = "MusicBrainz artist ID";
+
+	fn merge_func(src: &Value) -> Value {
+		merge_strings_with_comma(src)
+	}
+}
+
+pub struct MbAlbumArtistId;
+
+impl<'a> Tag<'a> for MbAlbumArtistId {
+	type TagType = &'a str;
+
+	fn tag_name<'b>() -> &'b str {
+		"musicbrainz-albumartistid"
+	}
+}
+
+impl CustomTag<'_> for MbAlbumArtistId {
+	const FLAG: TagFlag = TagFlag::Meta;
+	const NICK: &'static str = "album artist ID";
+	const DESCRIPTION: &'static str = "MusicBrainz album artist ID";
+
+	fn merge_func(src: &Value) -> Value {
+		merge_strings_with_comma(src)
+	}
+}