fix: unblock preroll on mpegtssrt output (async=false) (#504)

* fix: set async=false on mpegtssrt output srtsink to unblock preroll

In listener mode without a connected client, srtsink holds PAUSED->PLAYING
until the first buffer arrives, which blocks pipeline preroll. Matches the
pattern used by WHEP/WHIP/AES67 sinks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix: offset WHEP session count to clear input port labels

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Per Enstedt <per.enstedt@svt.se>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 3 people

backend/src/blocks/builtin/mpegtssrt.rs

@@ -233,6 +233,10 @@ impl BlockBuilder for MpegTsSrtOutputBuilder {
         // Fixed: 2025-12-01
         srtsink.set_property("sync", sync);
         srtsink.set_property("qos", true);
+        // async=false: don't block pipeline preroll waiting for the first buffer.
+        // In listener mode without a connected client, the sink would otherwise
+        // hold PAUSED->PLAYING indefinitely. Matches WHEP/WHIP/AES67 sinks.
+        srtsink.set_property("async", false);
 
         if has_auto_reconnect {
             info!(

frontend/src/webrtc_stats.rs

@@ -122,9 +122,12 @@ pub fn show_compact(ui: &mut Ui, stats: &WebRtcStats) {
         0.0
     };
 
-    // Build compact status line (centered)
+    // Build compact status line. Offset from the left edge so the text
+    // clears the input port labels (V0/A0) that are drawn just inside
+    // the block rect.
     ui.with_layout(egui::Layout::top_down(egui::Align::Center), |ui| {
         ui.horizontal(|ui| {
+            ui.add_space(30.0);
             // Session count with color indicator
             let color = if connected_count == session_count && session_count > 0 {
                 Color32::from_rgb(0, 180, 0)