From c83f00e7bfd209ed7793ac92afc769d0a4b349bd Mon Sep 17 00:00:00 2001
From: Niellune <niellune-sub@yandex.ru>
Date: Thu, 12 Jun 2025 20:52:01 +0300
Subject: [PATCH] Options to control decoding codec

---
 settings.txt    | 15 ++++++++++++++-
 src/decoder.cpp | 15 +++++++++++----
 src/settings.h  |  7 +++++++
 3 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/settings.txt b/settings.txt
index fc46cd7..115cc06 100644
--- a/settings.txt
+++ b/settings.txt
@@ -90,6 +90,11 @@
 # Enable vsync. This reduce tearing but can dramatically affect performance on low end systems 
 #vsync = false
 
+# Prefer HW decoding.
+# If you have input lag that means that your hardware decoder can't work in streaming mode
+# This is happening or Raspberry Pi Zero 2W. Disable this to use SW decoding for that case.
+#hw-decode = true
+
 # Corrects aspect of UI
 #aspect-correction = 1
 
@@ -153,4 +158,12 @@
 # 2 - all commands except data streams
 # 3 - include outgoing commands
 # 4 - log everything
-# protocol-debug = 0
\ No newline at end of file
+# protocol-debug = 0
+
+# Enable FFMPEG AV_CODEC_FLAG_LOW_DELAY for HW decoder.
+# Force low delay.
+#decode-low-delay = true
+
+# Enable FFMPEG AV_CODEC_FLAG2_FAST for HW decoder.
+# Allow non spec compliant speedup tricks.
+#decode-fast = false
\ No newline at end of file
diff --git a/src/decoder.cpp b/src/decoder.cpp
index b846eb9..e0cb487 100644
--- a/src/decoder.cpp
+++ b/src/decoder.cpp
@@ -49,7 +49,7 @@ AVCodecContext *Decoder::load_codec(AVCodecID codec_id)
     AVCodecContext *result = nullptr;
 
     // Try hardware-accelerated decoders by iterating registered codecs
-    while ((codec = av_codec_iterate(&iter)))
+    while ((codec = av_codec_iterate(&iter)) && Settings::hwDecode)
     {
         if (!av_codec_is_decoder(codec) || codec->id != codec_id)
             continue;
@@ -63,14 +63,21 @@ AVCodecContext *Decoder::load_codec(AVCodecID codec_id)
             break;
         }
 
+        if(Settings::codecLowDelay)
+            result->flags |= AV_CODEC_FLAG_LOW_DELAY;
+        if(Settings::codecFast)
+            result->flags2 |= AV_CODEC_FLAG2_FAST;
+
         int ret = avcodec_open2(result, codec, nullptr);
         if (ret == 0)
         {
             std::cout << "[Video] Using HW decoder: " << codec->name << std::endl;
+            if (result->codec->capabilities & AV_CODEC_CAP_DELAY)
+                std::cout << "[Video] Codec has AV_CODEC_CAP_DELAY and can introduce lags, consider use SW decoding" << std::endl;
             return result;
         }
 
-        std::cout << "[Video] Can't load HW codec " << codec->name << ": " << avErrorText(ret) << std::endl;
+        std::cout << "[Video] Can't load HW decoder " << codec->name << ": " << avErrorText(ret) << std::endl;
         avcodec_free_context(&result);
     }
 
@@ -78,7 +85,7 @@ AVCodecContext *Decoder::load_codec(AVCodecID codec_id)
     codec = avcodec_find_decoder(codec_id);
     if (!codec)
     {
-        std::cout << "[Video] Decoder not found for codec id " << codec_id << std::endl;
+        std::cout << "[Video] HW decoder not found for codec id " << codec_id << std::endl;
         return nullptr;
     }
 
@@ -92,7 +99,7 @@ AVCodecContext *Decoder::load_codec(AVCodecID codec_id)
     int ret = avcodec_open2(result, codec, nullptr);
     if (ret < 0)
     {
-        std::cout << "[Video] Failed to open software decoder " << codec->name << ": " << avErrorText(ret) << std::endl;
+        std::cout << "[Video] Failed to open SW decoder " << codec->name << ": " << avErrorText(ret) << std::endl;
         avcodec_free_context(&result);
         return nullptr;
     }
diff --git a/src/settings.h b/src/settings.h
index 6ff27ac..1bf43a5 100644
--- a/src/settings.h
+++ b/src/settings.h
@@ -33,6 +33,7 @@ public:
     // Application configuration section
     static inline Setting<int> fontSize{"font-size", 30};
     static inline Setting<bool> vsync{"vsync", false};
+    static inline Setting<bool> hwDecode{"hw-decode", true};
     static inline Setting<float> aspectCorrection{"aspect-correction", 1};
     static inline Setting<bool> fastScale{"fast-render-scale", false};
     static inline Setting<int> videoQueue{"video-buffer-size", 32};
@@ -51,6 +52,12 @@ public:
 
     // Debug section
     static inline Setting<int> protocolDebug{"protocol-debug", 0};
+    static inline Setting<float> codecLowDelay{"decode-low-delay", true};
+    static inline Setting<float> codecFast{"decode-fast", false};
+
+
+
+
 
     static void load(const std::string &filename);
     static void print();