transcriberbin: also support 608 inside 708

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1406>

docs/plugins/gst_plugins_cache.json

@@ -5566,7 +5566,7 @@
                     "mux-method": {
                         "blurb": "The method for muxing multiple transcription streams",
                         "conditionally-available": false,
-                        "construct": false,
+                        "construct": true,
                         "construct-only": false,
                         "controllable": false,
                         "default": "cea608 (0)",
@@ -5906,6 +5906,21 @@
                     }
                 ]
             },
+            "GstTranscriberBinMuxMethod": {
+                "kind": "enum",
+                "values": [
+                    {
+                        "desc": "Cea608",
+                        "name": "cea608",
+                        "value": "0"
+                    },
+                    {
+                        "desc": "Cea708",
+                        "name": "cea708",
+                        "value": "1"
+                    }
+                ]
+            },
             "GstTtToCea608Mode": {
                 "kind": "enum",
                 "values": [

video/closedcaption/src/transcriberbin/imp.rs

@@ -17,7 +17,7 @@ use std::sync::Mutex;
 
 use once_cell::sync::Lazy;
 
-use super::CaptionSource;
+use super::{CaptionSource, MuxMethod};
 
 static CAT: Lazy<gst::DebugCategory> = Lazy::new(|| {
     gst::DebugCategory::new(
@@ -38,15 +38,6 @@ const DEFAULT_MUX_METHOD: MuxMethod = MuxMethod::Cea608;
 
 const CEAX08MUX_LATENCY: gst::ClockTime = gst::ClockTime::from_mseconds(100);
 
-#[derive(Debug, Copy, Clone, Default, PartialEq, Eq, glib::Enum)]
-#[repr(u32)]
-#[enum_type(name = "GstTranscriberBinMuxMethod")]
-enum MuxMethod {
-    #[default]
-    Cea608,
-    Cea708,
-}
-
 /* One per language, including original */
 struct TranscriptionChannel {
     bin: gst::Bin,
@@ -176,7 +167,14 @@ impl TranscriberBin {
                                 "Multiple CEA-608 streams for a language are not supported"
                             );
                         }
-                        cea608_channel = Some(cea608.parse::<u32>()?);
+                        let channel = cea608.parse::<u32>()?;
+                        if (1..=4).contains(&channel) {
+                            cea608_channel = Some(channel);
+                        } else {
+                            anyhow::bail!(
+                                "CEA-608 channels only support values between 1 and 4 inclusive"
+                            );
+                        }
                     } else if let Some(cea708_service) = cc.strip_prefix("708_") {
                         if service_no.is_some() {
                             anyhow::bail!(
@@ -191,13 +189,12 @@ impl TranscriberBin {
                     }
                 }
                 let service_no = service_no.ok_or(anyhow!("No 708 caption service provided"))?;
-                // TODO: handle cea608
-                (
-                    gst::ElementFactory::make("tttocea708")
-                        .property("service-number", service_no)
-                        .build()?,
-                    format!("sink_{}", service_no),
-                )
+                let mut builder =
+                    gst::ElementFactory::make("tttocea708").property("service-number", service_no);
+                if let Some(channel) = cea608_channel {
+                    builder = builder.property("cea608-channel", channel);
+                }
+                (builder.build()?, format!("sink_{}", service_no))
             }
         };
         let capsfilter = gst::ElementFactory::make("capsfilter").build()?;

video/closedcaption/src/transcriberbin/mod.rs

@@ -20,13 +20,25 @@ pub enum CaptionSource {
     Inband,
 }
 
+#[derive(Debug, Copy, Clone, Default, PartialEq, Eq, glib::Enum)]
+#[repr(u32)]
+#[enum_type(name = "GstTranscriberBinMuxMethod")]
+enum MuxMethod {
+    #[default]
+    Cea608,
+    Cea708,
+}
+
 glib::wrapper! {
     pub struct TranscriberBin(ObjectSubclass<imp::TranscriberBin>) @extends gst::Bin, gst::Element, gst::Object;
 }
 
 pub fn register(plugin: &gst::Plugin) -> Result<(), glib::BoolError> {
     #[cfg(feature = "doc")]
-    CaptionSource::static_type().mark_as_plugin_api(gst::PluginAPIFlags::empty());
+    {
+        CaptionSource::static_type().mark_as_plugin_api(gst::PluginAPIFlags::empty());
+        MuxMethod::static_type().mark_as_plugin_api(gst::PluginAPIFlags::empty());
+    }
 
     gst::Element::register(
         Some(plugin),