From 426273129de7ea44f50492e79746b7daa45ece97 Mon Sep 17 00:00:00 2001
From: Zac Gaetano <Zgaetano@wilddragon.net>
Date: Sun, 31 May 2026 13:44:45 -0400
Subject: [PATCH] fix(playout): video-only HLS preview (broken audio time_base
 was the black-screen cause)

Definitive root cause of the black preview, found via server-side ffmpeg
decode of the live playlist:

  Error while decoding stream #0:1: Invalid data found (x57)
  [abuffer] Value inf for parameter 'time_base' ... time_base to value 1/0

Stream #0:1 is the AAC audio. CasparCG's real-time channel feeds the HLS
consumer an audio stream whose muxed time_base is 1/0 (infinity). ffmpeg
itself cannot decode the playlist, and hls.js silently fails to append the
fragment after demux, so the <video> stays at readyState 0 (black) even
though the video PTS is perfectly continuous and segments serve 200.

Fix: drop audio from the HLS confidence monitor (-an). The video track is
clean h264 and plays in hls.js. Program audio still rides the primary
SRT/RTMP/SDI/NDI output, which is unaffected.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 services/playout/src/playout-manager.js | 28 +++++++++++++++----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/services/playout/src/playout-manager.js b/services/playout/src/playout-manager.js
index 35f1f2f..32c4eda 100644
--- a/services/playout/src/playout-manager.js
+++ b/services/playout/src/playout-manager.js
@@ -169,16 +169,23 @@ export class PlayoutManager {
     // reloads forever ("sliding 0.00 / prev-sn na / MISSED") and never appends
     // a fragment, so the preview stays black.
     //
-    // Fix: force a constant output frame rate (-r 30000/1001 = 29.97 CFR). This
-    // regenerates uniform PTS and — critically — makes the frame-based GOP land
-    // on regular time boundaries: at 29.97 fps a 60-frame GOP (-g 60) is exactly
-    // 2.0s, so every keyframe (and therefore every HLS split at -hls_time 2) is
-    // a clean 2.0s boundary. The original used -g 60 WITHOUT -r, so "60 frames"
-    // varied with the channel's irregular feed rate and segments drifted.
+    // The HLS preview is a VIDEO-ONLY confidence monitor. We deliberately drop
+    // audio (-an).
     //
-    // NOTE: -force_key_frames does NOT work here — CasparCG's FFMPEG consumer
-    // routes args to the muxer, not the encoder, and logs it as "Unused option".
-    // The CFR rate + frame GOP is the combination that actually takes effect.
+    // Why: CasparCG's real-time channel feeds the FFMPEG consumer an audio
+    // stream whose muxed time_base comes out as 1/0 (infinity). ffmpeg itself
+    // can't decode the resulting playlist ("Invalid data ... abuffer: Value inf
+    // for parameter 'time_base'"), and hls.js silently fails to append the
+    // fragment after demux — the video element sits at readyState 0 and the
+    // preview stays black. Dropping audio removes the broken stream entirely;
+    // the remaining video track is clean h264 and plays in hls.js. A confidence
+    // monitor doesn't need audio — the real program audio rides the primary
+    // SRT/RTMP/SDI/NDI output, which is unaffected.
+    //
+    // NOTE: encoder options like -g / -r / -force_key_frames are NOT honored
+    // here — CasparCG's FFMPEG consumer applies args to the muxer, not the
+    // encoder (it logs "Unused option"). Segment cadence follows the channel's
+    // own keyframes; that's fine for a video-only preview.
     const out = `${HLS_DIR}/index.m3u8`;
     const args = [
       `FILE "${out}"`,
@@ -187,8 +194,7 @@ export class PlayoutManager {
       '-hls_list_size 8',
       '-hls_flags delete_segments+append_list+independent_segments',
       '-codec:v libx264 -preset:v veryfast -tune:v zerolatency -b:v 800k -maxrate 1M -bufsize 2M',
-      '-r 30000/1001 -g 60 -keyint_min 60 -sc_threshold 0',
-      '-codec:a aac -b:a 96k -ar 48000',
+      '-an',
       '-filter:v format=yuv420p',
     ].join(' ');
     await this.amcp.send(`ADD ${CHANNEL} ${args}`);