fmp4mux: Only allow caps-related header updates if header-update-mode=caps

In none mode nothing is expecting updated headers, in the other existing
modes the goal is to get an updated header at the end with the duration.

So add a new mode specifically for caps changes.

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

docs/plugins/gst_plugins_cache.json

@@ -3598,6 +3598,11 @@
                         "desc": "Update",
                         "name": "update",
                         "value": "2"
+                    },
+                    {
+                        "desc": "Caps",
+                        "name": "caps",
+                        "value": "3"
                     }
                 ]
             },

mux/fmp4/src/fmp4mux/imp.rs

@@ -921,14 +921,14 @@ impl FMP4Mux {
     }
 
     // Caps/tag changes are allowed only in case that the
-    // header-update-mode is None.
+    // header-update-mode is Caps.
     //
     // CAUTION: This function logs an error if operation is not
     // allowed so it should be evaluated only in case the caps/tags
     // would change otherwise (e. g. right-most operand in boolean
     // expressions).
     fn header_update_allowed(&self, reason: &str) -> bool {
-        if self.settings.lock().unwrap().header_update_mode == super::HeaderUpdateMode::None {
+        if self.settings.lock().unwrap().header_update_mode == super::HeaderUpdateMode::Caps {
             gst::debug!(
                 CAT,
                 imp = self,
@@ -3643,17 +3643,30 @@ impl FMP4Mux {
         let class = aggregator.class();
         let variant = class.as_ref().variant;
 
-        if settings.header_update_mode == super::HeaderUpdateMode::None && at_eos {
+        if [super::HeaderUpdateMode::None, super::HeaderUpdateMode::Caps]
+            .contains(&settings.header_update_mode)
+            && at_eos
+        {
             return Ok(None);
         }
 
         assert!(!at_eos || state.streams.iter().all(|s| s.queued_gops.is_empty()));
 
-        let duration = state
-            .end_pts
-            .opt_checked_sub(state.earliest_pts)
-            .ok()
-            .flatten();
+        let duration = if at_eos
+            && [
+                super::HeaderUpdateMode::Update,
+                super::HeaderUpdateMode::Rewrite,
+            ]
+            .contains(&settings.header_update_mode)
+        {
+            state
+                .end_pts
+                .opt_checked_sub(state.earliest_pts)
+                .ok()
+                .flatten()
+        } else {
+            None
+        };
 
         let streams = state
             .streams
@@ -3750,7 +3763,7 @@ impl FMP4Mux {
         match updated_header {
             Ok(Some((buffer_list, caps))) => {
                 match settings.header_update_mode {
-                    super::HeaderUpdateMode::None => unreachable!(),
+                    super::HeaderUpdateMode::None | super::HeaderUpdateMode::Caps => unreachable!(),
                     super::HeaderUpdateMode::Rewrite => {
                         let mut q = gst::query::Seeking::new(gst::Format::Bytes);
                         if self.obj().src_pad().peer_query(&mut q) && q.result().0 {

mux/fmp4/src/fmp4mux/mod.rs

@@ -326,14 +326,51 @@ pub(crate) struct FragmentOffset {
     offset: u64,
 }
 
+/**
+ * GstFMP4MuxHeaderUpdateMode:
+ *
+ * How and when updating of the header (`moov`, initialization segment) is allowed.
+ */
 #[allow(clippy::upper_case_acronyms)]
 #[derive(Debug, Clone, Copy, PartialEq, Eq, glib::Enum)]
 #[repr(i32)]
 #[enum_type(name = "GstFMP4MuxHeaderUpdateMode")]
 pub(crate) enum HeaderUpdateMode {
+    /**
+     * GstFMP4MuxHeaderUpdateMode:none:
+     *
+     * Don't allow and do any header updates at all.
+     *
+     * Caps changes are not allowed in this mode.
+     */
     None,
+    /**
+     * GstFMP4MuxHeaderUpdateMode:rewrite:
+     *
+     * Try rewriting the initial header with the overall duration at the very end.
+     *
+     * Caps changes are not allowed in this mode.
+     */
     Rewrite,
+    /**
+     * GstFMP4MuxHeaderUpdateMode:update:
+     *
+     * Send an updated version of the initial header with the overall duration at
+     * the very end.
+     *
+     * Caps changes are not allowed in this mode.
+     */
     Update,
+    /**
+     * GstFMP4MuxHeaderUpdateMode:caps:
+     *
+     * Send an updated header whenever caps or tag changes are pending that affect the initial
+     * header. The updated header does not have the duration set and will always be followed by a
+     * new fragment.
+     *
+     * Since: plugins-rs-0.14.0
+     */
+    Caps,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, glib::Enum, Default)]

mux/fmp4/tests/tests.rs

@@ -2501,6 +2501,10 @@ fn test_caps_change_at_gop_boundary() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -2541,6 +2545,10 @@ fn test_language_change_at_gop_boundary() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -2603,6 +2611,10 @@ fn test_caps_change_at_gop_boundary_multi_stream() {
     let mut h1 = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
     let mut h2 = gst_check::Harness::with_element(&h1.element().unwrap(), Some("sink_1"), None);
 
+    h1.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps1 = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -2770,6 +2782,10 @@ fn test_caps_change_at_gop_boundary_chunked_multi_stream() {
     let mut h1 = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
     let mut h2 = gst_check::Harness::with_element(&h1.element().unwrap(), Some("sink_1"), None);
 
+    h1.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps1 = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -2918,6 +2934,10 @@ fn test_caps_change_at_gop_boundary_compatible() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1280i32)
         .field("height", 720i32)
@@ -2959,6 +2979,10 @@ fn test_caps_change_at_gop_boundary_not_allowed() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -3004,6 +3028,10 @@ fn test_caps_change_within_gop() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -3044,6 +3072,10 @@ fn test_caps_change_within_gop_start_without_key() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -3083,6 +3115,10 @@ fn test_caps_change_within_gop_chunked() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -3130,6 +3166,10 @@ fn test_caps_change_within_gop_no_key() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)
@@ -3171,6 +3211,10 @@ fn test_caps_change_before_first_frame() {
 
     let mut h = gst_check::Harness::with_padnames("isofmp4mux", Some("sink_0"), Some("src"));
 
+    h.element()
+        .unwrap()
+        .set_property_from_str("header-update-mode", "caps");
+
     let caps = gst::Caps::builder("video/x-h264")
         .field("width", 1920i32)
         .field("height", 1080i32)