From 26febc41d6dded0baa3bb98bae00410c3eda6f4a Mon Sep 17 00:00:00 2001
From: Johanness <mrjitten@protonmail.com>
Date: Sat, 30 May 2026 23:21:13 +0300
Subject: [PATCH] decklink-out: preroll frames before StartScheduledPlayback,
 detect output format

---
 nodes/decklink-out/src/decklink_out_node.cpp | 66 +++++++++++++-------
 nodes/decklink-out/src/decklink_out_node.hpp |  2 +
 2 files changed, 44 insertions(+), 24 deletions(-)

diff --git a/nodes/decklink-out/src/decklink_out_node.cpp b/nodes/decklink-out/src/decklink_out_node.cpp
index 1374256..4ff620a 100644
--- a/nodes/decklink-out/src/decklink_out_node.cpp
+++ b/nodes/decklink-out/src/decklink_out_node.cpp
@@ -126,20 +126,6 @@ bool DeckLinkOutNode::open_device() {
     callback_ = std::make_unique<OutputCallback>(*this);
     output_->SetScheduledFrameCompletionCallback(callback_.get());
 
-    {
-        BMDDisplayMode actual_mode = bmdModeUnknown;
-        bool supported = false;
-        auto hr = output_->DoesSupportVideoMode(bmdVideoConnectionUnspecified, display_mode_, bmdFormat10BitYUV,
-            bmdNoVideoOutputConversion, bmdSupportedVideoModeDefault, &actual_mode, &supported);
-        if (hr == S_OK) {
-            spdlog::info("DeckLink-out: mode 0x{:x} V210 supported={} actual=0x{:x}",
-                        static_cast<uint32_t>(display_mode_), supported, static_cast<uint32_t>(actual_mode));
-            if (!supported) {
-                spdlog::error("DeckLink-out: display mode not supported for V210 output");
-            }
-        }
-    }
-
     if (output_->EnableVideoOutput(display_mode_, bmdVideoOutputFlagDefault) != S_OK) {
         spdlog::error("DeckLink-out: failed to enable video output");
         return false;
@@ -171,6 +157,39 @@ bool DeckLinkOutNode::open_device() {
                      is_interlaced_);
     }
 
+    preroll_frames_ = 3;
+    for (int i = 0; i < preroll_frames_; ++i) {
+        IDeckLinkMutableVideoFrame* frame = nullptr;
+        int32_t out_row_bytes = out_width_ * 16 / 6;
+        if (output_->CreateVideoFrame(out_width_, out_height_, out_row_bytes,
+                                       bmdFormat10BitYUV, bmdFrameFlagDefault, &frame) != S_OK || !frame) {
+            out_row_bytes = out_width_ * 2;
+            if (output_->CreateVideoFrame(out_width_, out_height_, out_row_bytes,
+                                           bmdFormat8BitYUV, bmdFrameFlagDefault, &frame) != S_OK || !frame) {
+                spdlog::error("DeckLink-out: failed to create preroll frame");
+                return false;
+            }
+            spdlog::info("DeckLink-out: using 8BitYUV output format");
+            output_format_ = bmdFormat8BitYUV;
+        } else {
+            output_format_ = bmdFormat10BitYUV;
+        }
+        IDeckLinkVideoBuffer* buf = nullptr;
+        if (frame->QueryInterface(IID_IDeckLinkVideoBuffer, (void**)&buf) == S_OK && buf) {
+            buf->StartAccess(bmdBufferAccessWrite);
+            void* dst = nullptr;
+            buf->GetBytes(&dst);
+            if (dst) {
+                std::memset(dst, 0, out_row_bytes * out_height_);
+            }
+            buf->EndAccess(bmdBufferAccessWrite);
+            buf->Release();
+        }
+        auto stream_time = i * frame_duration_;
+        output_->ScheduleVideoFrame(frame, stream_time, frame_duration_, time_scale_);
+        frame->Release();
+    }
+
     if (output_->StartScheduledPlayback(0, time_scale_, 1.0) != S_OK) {
         spdlog::error("DeckLink-out: failed to start scheduled playback");
         return false;
@@ -201,24 +220,23 @@ void DeckLinkOutNode::schedule_frame(void* mxl_payload, long width, long height,
     if (!output_) return;
 
     int32_t out_row_bytes = 0;
-    HRESULT row_hr = output_->RowBytesForPixelFormat(bmdFormat10BitYUV, width, &out_row_bytes);
-    if (row_hr != S_OK || out_row_bytes <= 0) {
-        spdlog::warn("DeckLink-out: RowBytesForPixelFormat failed hr=0x{:08x}", static_cast<uint32_t>(row_hr));
-        out_row_bytes = ((width + 5) / 6) * 16;
+    if (output_format_ == bmdFormat10BitYUV) {
+        if (output_->RowBytesForPixelFormat(bmdFormat10BitYUV, width, &out_row_bytes) != S_OK || out_row_bytes <= 0) {
+            out_row_bytes = ((width + 5) / 6) * 16;
+        }
+    } else {
+        out_row_bytes = width * 2;
     }
 
     IDeckLinkMutableVideoFrame* frame = nullptr;
-    HRESULT hr = output_->CreateVideoFrame(width, height, out_row_bytes, bmdFormat10BitYUV,
+    HRESULT hr = output_->CreateVideoFrame(width, height, out_row_bytes, output_format_,
                                    bmdFrameFlagDefault, &frame);
     if (hr != S_OK || !frame) {
         if (create_fail_count_ < 5) {
-            spdlog::error("DeckLink-out: CreateVideoFrame {}x{} row_bytes={} fmt=V210 hr=0x{:08x}",
-                         width, height, out_row_bytes, static_cast<uint32_t>(hr));
+            spdlog::error("DeckLink-out: CreateVideoFrame {}x{} row_bytes={} fmt=0x{:x} hr=0x{:08x}",
+                         width, height, out_row_bytes, static_cast<uint32_t>(output_format_), static_cast<uint32_t>(hr));
             create_fail_count_++;
         }
-        if (create_fail_count_ == 5) {
-            spdlog::error("DeckLink-out: suppressing further CreateVideoFrame errors");
-        }
         return;
     }
 
diff --git a/nodes/decklink-out/src/decklink_out_node.hpp b/nodes/decklink-out/src/decklink_out_node.hpp
index 4a369db..b08b675 100644
--- a/nodes/decklink-out/src/decklink_out_node.hpp
+++ b/nodes/decklink-out/src/decklink_out_node.hpp
@@ -55,6 +55,8 @@ private:
     IDeckLinkOutput* output_ = nullptr;
     BMDTimeValue frame_duration_ = 1000;
     BMDTimeScale time_scale_ = 50000;
+    BMDPixelFormat output_format_ = bmdFormat10BitYUV;
+    int preroll_frames_ = 3;
 
     std::atomic<bool> playing_{false};
     int create_fail_count_ = 0;