video: sync capture: resend frame if needed to avoid capture delay

src/main.cpp

@@ -45,6 +45,7 @@ bl::sources::severity_logger<int> error(4);   // Recoverable errors
 bl::sources::severity_logger<int> fatal(5);   // Unrecoverable errors
 
 bool display_cursor = true;
+bool force_callback = false;
 
 using text_sink = bl::sinks::asynchronous_sink<bl::sinks::text_ostream_backend>;
 boost::shared_ptr<text_sink> sink;

src/main.h

@@ -12,6 +12,7 @@
 
 extern util::ThreadPool task_pool;
 extern bool display_cursor;
+extern bool force_callback;
 
 extern boost::log::sources::severity_logger<int> verbose;
 extern boost::log::sources::severity_logger<int> debug;

src/platform/windows/display_vram.cpp

@@ -573,14 +573,16 @@ capture_e display_vram_t::capture(snapshot_cb_t &&snapshot_cb, std::shared_ptr<:
     }
     next_frame = now + delay;
 
-    auto status = snapshot(img.get(), 1000ms, *cursor);
+    auto status = snapshot(img.get(), force_callback ? std::chrono::duration_cast<std::chrono::milliseconds>(delay * 2) : 1000ms, *cursor);
     switch(status) {
     case platf::capture_e::reinit:
     case platf::capture_e::error:
       return status;
     case platf::capture_e::timeout:
-      std::this_thread::sleep_for(1ms);
-      continue;
+      if(!force_callback) {
+        std::this_thread::sleep_for(1ms);
+        continue;
+      }
     case platf::capture_e::ok:
       img = snapshot_cb(img);
       break;
@@ -885,4 +887,4 @@ int init() {
 
   return 0;
 }
-} // namespace platf::dxgi
+} // namespace platf::dxgi

src/video.cpp

@@ -71,7 +71,7 @@ util::Either<buffer_t, int> dxgi_make_hwdevice_ctx(platf::hwdevice_t *hwdevice_c
 util::Either<buffer_t, int> vaapi_make_hwdevice_ctx(platf::hwdevice_t *hwdevice_ctx);
 util::Either<buffer_t, int> cuda_make_hwdevice_ctx(platf::hwdevice_t *hwdevice_ctx);
 
-int hwframe_ctx(ctx_t &ctx, buffer_t &hwdevice, AVPixelFormat format);
+int hwframe_ctx(ctx_t &ctx, buffer_t &hwdevice, AVPixelFormat format, bool amf_lowlatency);
 
 class swdevice_t : public platf::hwdevice_t {
 public:
@@ -240,6 +240,7 @@ enum flag_e {
   H264_ONLY         = 0x02, // When HEVC is too heavy
   LIMITED_GOP_SIZE  = 0x04, // Some encoders don't like it when you have an infinite GOP_SIZE. *cough* VAAPI *cough*
   SINGLE_SLICE_ONLY = 0x08, // Never use multiple slices <-- Older intel iGPU's ruin it for everyone else :P
+  FORCE_CALLBACK    = 0x10, // Force callbacks with short timeouts for encoders that don't perform well with callback-based capture
 };
 
 struct encoder_t {
@@ -438,7 +439,7 @@ static encoder_t nvenc {
     "h264_nvenc"s,
   },
 #ifdef _WIN32
-  DEFAULT,
+  FORCE_CALLBACK,
   dxgi_make_hwdevice_ctx
 #else
   PARALLEL_ENCODING,
@@ -474,7 +475,7 @@ static encoder_t amdvce {
     std::make_optional<encoder_t::option_t>({ "qp_p"s, &config::video.qp }),
     "h264_amf"s,
   },
-  DEFAULT,
+  FORCE_CALLBACK,
   dxgi_make_hwdevice_ctx
 };
 #endif
@@ -931,7 +932,7 @@ std::optional<session_t> make_session(const encoder_t &encoder, const config_t &
     }
 
     hwdevice_ctx = std::move(buf_or_error.left());
-    if(hwframe_ctx(ctx, hwdevice_ctx, sw_fmt)) {
+    if(hwframe_ctx(ctx, hwdevice_ctx, sw_fmt, (encoder.name == "amdvce"sv))) {
       return std::nullopt;
     }
 
@@ -1404,6 +1405,7 @@ void capture(
   void *channel_data) {
 
   auto idr_events = mail->event<bool>(mail::idr);
+  force_callback  = encoders.front().flags & FORCE_CALLBACK;
 
   idr_events->raise(true);
   if(encoders.front().flags & PARALLEL_ENCODING) {
@@ -1680,7 +1682,7 @@ int init() {
   return 0;
 }
 
-int hwframe_ctx(ctx_t &ctx, buffer_t &hwdevice, AVPixelFormat format) {
+int hwframe_ctx(ctx_t &ctx, buffer_t &hwdevice, AVPixelFormat format, bool amf_lowlatency) {
   buffer_t frame_ref { av_hwframe_ctx_alloc(hwdevice.get()) };
 
   auto frame_ctx               = (AVHWFramesContext *)frame_ref->data;
@@ -1694,6 +1696,12 @@ int hwframe_ctx(ctx_t &ctx, buffer_t &hwdevice, AVPixelFormat format) {
     return err;
   }
 
+  if(amf_lowlatency) {
+    // reduce amf encoder's hw buffers from 16 -> 2 to minimize buffered frames
+    // note: pool size is deliberately set after initialization
+    frame_ctx->initial_pool_size = 3;
+  }
+
   ctx->hw_frames_ctx = av_buffer_ref(frame_ref.get());
 
   return 0;