ensure we initialize encoder correctly and send keyframe first

Author: chenosaurus

webrtc-sys/src/v4l2/v4l2_h264_encoder_wrapper.cpp

@@ -288,6 +288,12 @@ bool V4l2H264EncoderWrapper::Initialize(int width,
       fd_ = -1;
       return false;
     }
+
+    // Zero-fill the buffer so unprimed slots contain valid black YUV data
+    // rather than random memory. The Pi 4 V4L2 M2M encoder may reference
+    // multiple output buffers internally before the pipeline is fully primed,
+    // causing distorted/green frames if buffers contain garbage.
+    memset(output_buffers_[i].start, 0, output_buffers_[i].length);
   }
 
   // --- Request and mmap capture buffers (encoder output) ---
@@ -373,6 +379,7 @@ bool V4l2H264EncoderWrapper::Initialize(int width,
                    << " @ " << framerate << " fps, bitrate " << bitrate;
   initialized_ = true;
   next_output_index_ = 0;
+  first_frame_ = true;
   return true;
 }
 
@@ -418,6 +425,13 @@ bool V4l2H264EncoderWrapper::Encode(const uint8_t* y,
     return false;
   }
 
+  // Always force an IDR on the very first frame so the decoder starts clean,
+  // avoiding startup artifacts from the encoder pipeline not being primed yet.
+  if (first_frame_) {
+    forceIDR = true;
+    first_frame_ = false;
+  }
+
   // Request a keyframe if needed.
   if (forceIDR) {
     v4l2_control ctrl = {};

webrtc-sys/src/v4l2/v4l2_h264_encoder_wrapper.h

@@ -97,6 +97,10 @@ class V4l2H264EncoderWrapper {
 
   // Index of the next output buffer to use (round-robin).
   int next_output_index_ = 0;
+
+  // Force the first encoded frame to be an IDR keyframe so the decoder
+  // starts with a clean reference and doesn't show startup artifacts.
+  bool first_frame_ = true;
 };
 
 }  // namespace livekit_ffi