Fix YouTube relay instabile e timer LIVE a zero in app

ffmpeg: probesize/analyzeduration su _air, restart più rapido e avvio relay
al go_live. App: sincronizza started_at dal server e fallback al passaggio live.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/services/streams/youtube_relay.rb

@@ -56,10 +56,13 @@ module Streams
         return if session.stream_key.blank?
         return unless Streams::OverlayRelay.running?(session.id)
 
+        pid = pid_for(session.id)
+        clear_pid(session.id) if pid.present? && !process_alive?(pid.to_i)
+
         return if running?(session.id)
 
         last_restart = redis.get(restart_debounce_key(session.id)).to_i
-        return if last_restart.positive? && (Time.now.to_i - last_restart) < 20
+        return if last_restart.positive? && (Time.now.to_i - last_restart) < 5
 
         start(session)
         redis.set(restart_debounce_key(session.id), Time.now.to_i, ex: 300)
@@ -75,6 +78,7 @@ module Streams
         [
           "ffmpeg", "-nostdin", "-hide_banner", "-loglevel", "warning",
           "-fflags", "+genpts+discardcorrupt", "-use_wallclock_as_timestamps", "1",
+          "-analyzeduration", "10000000", "-probesize", "10000000",
           "-rw_timeout", "15000000",
           "-i", intake,
           "-f", "lavfi", "-i", "anullsrc=channel_layout=mono:sample_rate=48000",