mp4mux: Store language tags per stream and not globally

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/2193>

mux/mp4/src/mp4mux/boxes.rs

@@ -433,7 +433,7 @@ fn language_code(lang: impl std::borrow::Borrow<[u8; 3]>) -> u16 {
 
 fn write_mdhd(
     v: &mut Vec<u8>,
-    header: &super::Header,
+    _header: &super::Header,
     stream: &super::Stream,
     creation_time: u64,
 ) -> Result<(), Error> {
@@ -456,7 +456,7 @@ fn write_mdhd(
     v.extend(duration.to_be_bytes());
 
     // Language as ISO-639-2/T
-    if let Some(lang) = header.language_code {
+    if let Some(lang) = stream.language_code {
         v.extend(language_code(lang).to_be_bytes());
     } else {
         v.extend(language_code(b"und").to_be_bytes());

mux/mp4/src/mp4mux/imp.rs

@@ -148,6 +148,9 @@ struct Stream {
 
     extra_header_data: Option<Vec<u8>>,
 
+    /// Language code from tags
+    language_code: Option<[u8; 3]>,
+
     /// Orientation from tags
     orientation: Option<ImageOrientation>,
 }
@@ -282,9 +285,6 @@ struct State {
 
     /// Size of the `mdat` as written so far.
     mdat_size: u64,
-
-    /// Language code from tags
-    language_code: Option<[u8; 3]>,
 }
 
 #[derive(Default)]
@@ -1220,6 +1220,7 @@ impl MP4Mux {
                 end_pts: None,
                 running_time_utc_time_mapping: None,
                 extra_header_data: None,
+                language_code: None,
                 orientation: None,
             });
         }
@@ -1434,7 +1435,9 @@ impl AggregatorImpl for MP4Mux {
                 self.parent_sink_event_pre_queue(aggregator_pad, event)
             }
             EventView::Tag(ev) => {
-                if let Some(tag_value) = ev.tag().get::<gst::tags::LanguageCode>() {
+                let tag = ev.tag();
+
+                if let Some(tag_value) = tag.get::<gst::tags::LanguageCode>() {
                     let lang = tag_value.get();
                     gst::trace!(
                         CAT,
@@ -1451,7 +1454,21 @@ impl AggregatorImpl for MP4Mux {
                         for (out, c) in Iterator::zip(language_code.iter_mut(), lang.chars()) {
                             *out = c as u8;
                         }
-                        state.language_code = Some(language_code);
+
+                        if tag.scope() == gst::TagScope::Global {
+                            gst::info!(
+                                CAT,
+                                imp = self,
+                                "Language tags scoped 'global' are considered stream tags",
+                            );
+                        }
+
+                        for stream in &mut state.streams {
+                            if &stream.sinkpad == aggregator_pad {
+                                stream.language_code = Some(language_code);
+                                break;
+                            }
+                        }
                     }
                 } else if let Some(tag_value) = ev.tag().get::<gst::tags::ImageOrientation>() {
                     let orientation = tag_value.get();
@@ -1736,6 +1753,7 @@ impl AggregatorImpl for MP4Mux {
                     image_sequence: stream.image_sequence_mode(),
                     chunks: stream.chunks,
                     extra_header_data: stream.extra_header_data.clone(),
+                    language_code: stream.language_code,
                     orientation: stream.orientation,
                 });
             }
@@ -1744,7 +1762,6 @@ impl AggregatorImpl for MP4Mux {
                 variant: self.obj().class().as_ref().variant,
                 movie_timescale: settings.movie_timescale,
                 streams,
-                language_code: state.language_code,
             })
             .map_err(|err| {
                 gst::error!(CAT, imp = self, "Failed to create moov box: {err}");

mux/mp4/src/mp4mux/mod.rs

@@ -203,6 +203,9 @@ pub(crate) struct Stream {
     // More data to be included in the fragmented stream header
     extra_header_data: Option<Vec<u8>>,
 
+    // Language code from tags
+    language_code: Option<[u8; 3]>,
+
     /// Orientation from tags
     orientation: Option<ImageOrientation>,
 
@@ -220,7 +223,6 @@ pub(crate) struct Header {
     /// Pre-defined movie timescale if not 0.
     movie_timescale: u32,
     streams: Vec<Stream>,
-    language_code: Option<[u8; 3]>,
 }
 
 #[allow(clippy::upper_case_acronyms)]