diff --git a/src/platform/macos/nv12_zero_device.cpp b/src/platform/macos/nv12_zero_device.cpp
index 881c86aa..f376bdcd 100644
--- a/src/platform/macos/nv12_zero_device.cpp
+++ b/src/platform/macos/nv12_zero_device.cpp
@@ -26,9 +26,17 @@ namespace platf {
   nv12_zero_device::convert(platf::img_t &img) {
     av_img_t *av_img = (av_img_t *) &img;
 
+    // Release any existing CVPixelBuffer previously retained for encoding
     av_buffer_unref(&av_frame->buf[0]);
 
+    // Attach an AVBufferRef to this frame which will retain ownership of the CVPixelBuffer
+    // until av_buffer_unref() is called (above) or the frame is freed with av_frame_free().
+    //
+    // The presence of the AVBufferRef allows FFmpeg to simply add a reference to the buffer
+    // rather than having to perform a deep copy of the data buffers in avcodec_send_frame().
     av_frame->buf[0] = av_buffer_create((uint8_t *) CFRetain(av_img->pixel_buffer->buf), 0, free_buffer, NULL, 0);
+
+    // Place a CVPixelBufferRef at data[3] as required by AV_PIX_FMT_VIDEOTOOLBOX
     av_frame->data[3] = (uint8_t *) av_img->pixel_buffer->buf;
 
     return 0;