fix(macos): drop max_ref_frames=1 for h264_videotoolbox and enable PARALLEL_ENCODING (#5200)

src/video.cpp

@@ -1134,12 +1134,16 @@ namespace video {
     },
     {
       // Common options
+      // Note: max_ref_frames is intentionally omitted for H.264 because
+      // VideoToolbox on Apple Silicon produces all-IDR output when
+      // ReferenceBufferCount=1 is set for H.264, causing massive bandwidth
+      // inflation (~3x) and frame drops. HEVC and AV1 are unaffected and
+      // retain max_ref_frames=1. See LizardByte/Sunshine#5013.
       {
         {"allow_sw"s, &config::video.vt.vt_allow_sw},
         {"require_sw"s, &config::video.vt.vt_require_sw},
         {"realtime"s, &config::video.vt.vt_realtime},
         {"prio_speed"s, 1},
-        {"max_ref_frames"s, 1},
       },
       {},  // SDR-specific options
       {},  // HDR-specific options
@@ -1151,7 +1155,7 @@ namespace video {
       },
       "h264_videotoolbox"s,
     },
-    DEFAULT
+    PARALLEL_ENCODING
   };
 #endif