Add option to enforce a minimum latency to improve frame pacing

app/cli/commandlineparser.cpp

@@ -374,6 +374,7 @@ void StreamCommandLineParser::parse(const QStringList &args, StreamingPreference
     parser.addChoiceOption("capture-system-keys", "capture system key combos", m_CaptureSysKeysModeMap.keys());
     parser.addChoiceOption("video-codec", "video codec", m_VideoCodecMap.keys());
     parser.addChoiceOption("video-decoder", "video decoder", m_VideoDecoderMap.keys());
+    parser.addValueOption("minimum-latency", "Minimum latency");
 
     if (!parser.parse(args)) {
         parser.showError(parser.errorText());
@@ -500,6 +501,13 @@ void StreamCommandLineParser::parse(const QStringList &args, StreamingPreference
         preferences->videoDecoderSelection = mapValue(m_VideoDecoderMap, parser.getChoiceOptionValue("video-decoder"));
     }
 
+    if (parser.isSet("minimum-latency")) {
+        preferences->minimumLatency = parser.getIntOption("minimum-latency");
+        if (!inRange(preferences->minimumLatency, 0, 50)) {
+            parser.showError("Minimum latency must be in range: 0 - 50");
+        }
+    }
+
     // This method will not return and terminates the process if --version or
     // --help is specified
     parser.handleHelpAndVersionOptions();

app/gui/SettingsView.qml

@@ -812,6 +812,45 @@ Flickable {
                     ToolTip.visible: hovered
                     ToolTip.text: qsTr("Frame pacing reduces micro-stutter by delaying frames that come in too early")
                 }
+
+                Label {
+                    width: parent.width
+                    id: minimumLatencyTitle
+                    text: qsTr("Minimum latency:")
+                    font.pointSize: 12
+                    wrapMode: Text.Wrap
+                }
+
+                Label {
+                    width: parent.width
+                    id: minimumLatencyDesc
+                    text: qsTr("A lower bound on display latency. Set higher to account for more jitter in your connection, at the cost of increased display latency.")
+                    font.pointSize: 9
+                    wrapMode: Text.Wrap
+                }
+
+                Slider {
+                    id: minimumLatencySlider
+
+                    value: StreamingPreferences.minimumLatency
+
+                    stepSize: 1
+                    from : 0
+                    to: 50
+
+                    snapMode: "SnapOnRelease"
+                    width: Math.min(minimumLatencyDesc.implicitWidth, parent.width)
+
+                    onValueChanged: {
+                        minimumLatencyTitle.text = qsTr("Minimum latency: %1 msec").arg(value)
+                        StreamingPreferences.minimumLatency = value
+                    }
+
+                    Component.onCompleted: {
+                        // Refresh the text after translations change
+                        languageChanged.connect(onValueChanged)
+                    }
+                }
             }
         }
 

app/settings/streamingpreferences.cpp

@@ -45,6 +45,7 @@
 #define SER_CAPTURESYSKEYS "capturesyskeys"
 #define SER_KEEPAWAKE "keepawake"
 #define SER_LANGUAGE "language"
+#define SER_MINIMUMLATENCY "minimumlatency"
 
 #define CURRENT_DEFAULT_VER 2
 
@@ -122,6 +123,7 @@ void StreamingPreferences::reload()
                                                                                                                  : UIDisplayMode::UI_MAXIMIZED)).toInt());
     language = static_cast<Language>(settings.value(SER_LANGUAGE,
                                                     static_cast<int>(Language::LANG_AUTO)).toInt());
+    minimumLatency = settings.value(SER_MINIMUMLATENCY, 0).toInt();
 
 
     // Perform default settings updates as required based on last default version
@@ -295,6 +297,7 @@ void StreamingPreferences::save()
     settings.setValue(SER_SWAPFACEBUTTONS, swapFaceButtons);
     settings.setValue(SER_CAPTURESYSKEYS, captureSysKeysMode);
     settings.setValue(SER_KEEPAWAKE, keepAwake);
+    settings.setValue(SER_MINIMUMLATENCY, minimumLatency);
 }
 
 int StreamingPreferences::getDefaultBitrate(int width, int height, int fps)

app/settings/streamingpreferences.h

@@ -134,7 +134,8 @@ class StreamingPreferences : public QObject
     Q_PROPERTY(bool swapFaceButtons MEMBER swapFaceButtons NOTIFY swapFaceButtonsChanged)
     Q_PROPERTY(bool keepAwake MEMBER keepAwake NOTIFY keepAwakeChanged)
     Q_PROPERTY(CaptureSysKeysMode captureSysKeysMode MEMBER captureSysKeysMode NOTIFY captureSysKeysModeChanged)
-    Q_PROPERTY(Language language MEMBER language NOTIFY languageChanged);
+    Q_PROPERTY(Language language MEMBER language NOTIFY languageChanged)
+    Q_PROPERTY(int minimumLatency MEMBER minimumLatency NOTIFY minimumLatencyChanged);
 
     Q_INVOKABLE bool retranslate();
 
@@ -172,6 +173,7 @@ class StreamingPreferences : public QObject
     UIDisplayMode uiDisplayMode;
     Language language;
     CaptureSysKeysMode captureSysKeysMode;
+    int minimumLatency;
 
 signals:
     void displayModeChanged();
@@ -204,6 +206,7 @@ class StreamingPreferences : public QObject
     void captureSysKeysModeChanged();
     void keepAwakeChanged();
     void languageChanged();
+    void minimumLatencyChanged();
 
 private:
     QString getSuffixFromLanguage(Language lang);

app/streaming/session.cpp

@@ -256,7 +256,8 @@ void Session::clSetControllerLED(uint16_t controllerNumber, uint8_t r, uint8_t g
 
 bool Session::chooseDecoder(StreamingPreferences::VideoDecoderSelection vds,
                             SDL_Window* window, int videoFormat, int width, int height,
-                            int frameRate, bool enableVsync, bool enableFramePacing, bool testOnly, IVideoDecoder*& chosenDecoder)
+                            int frameRate, bool enableVsync, bool enableFramePacing, bool testOnly, IVideoDecoder*& chosenDecoder,
+                            int minimumLatency)
 {
     DECODER_PARAMETERS params;
 
@@ -274,6 +275,7 @@ bool Session::chooseDecoder(StreamingPreferences::VideoDecoderSelection vds,
     params.enableFramePacing = enableFramePacing;
     params.testOnly = testOnly;
     params.vds = vds;
+    params.minimumLatency = minimumLatency;
 
     SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
                 "V-sync %s",
@@ -376,7 +378,7 @@ void Session::getDecoderInfo(SDL_Window* window,
     // Try an HEVC Main10 decoder first to see if we have HDR support
     if (chooseDecoder(StreamingPreferences::VDS_FORCE_HARDWARE,
                       window, VIDEO_FORMAT_H265_MAIN10, 1920, 1080, 60,
-                      false, false, true, decoder)) {
+                      false, false, true, decoder, 0)) {
         isHardwareAccelerated = decoder->isHardwareAccelerated();
         isFullScreenOnly = decoder->isAlwaysFullScreen();
         isHdrSupported = decoder->isHdrSupported();
@@ -389,7 +391,7 @@ void Session::getDecoderInfo(SDL_Window* window,
     // Try an AV1 Main10 decoder next to see if we have HDR support
     if (chooseDecoder(StreamingPreferences::VDS_FORCE_HARDWARE,
                       window, VIDEO_FORMAT_AV1_MAIN10, 1920, 1080, 60,
-                      false, false, true, decoder)) {
+                      false, false, true, decoder, 0)) {
         // If we've got a working AV1 Main 10-bit decoder, we'll enable the HDR checkbox
         // but we will still continue probing to get other attributes for HEVC or H.264
         // decoders. See the AV1 comment at the top of the function for more info.
@@ -405,7 +407,7 @@ void Session::getDecoderInfo(SDL_Window* window,
     // Try a regular hardware accelerated HEVC decoder now
     if (chooseDecoder(StreamingPreferences::VDS_FORCE_HARDWARE,
                       window, VIDEO_FORMAT_H265, 1920, 1080, 60,
-                      false, false, true, decoder)) {
+                      false, false, true, decoder, 0)) {
         isHardwareAccelerated = decoder->isHardwareAccelerated();
         isFullScreenOnly = decoder->isAlwaysFullScreen();
         maxResolution = decoder->getDecoderMaxResolution();
@@ -418,7 +420,7 @@ void Session::getDecoderInfo(SDL_Window* window,
 #if 0 // See AV1 comment at the top of this function
     if (chooseDecoder(StreamingPreferences::VDS_FORCE_HARDWARE,
                       window, VIDEO_FORMAT_AV1_MAIN8, 1920, 1080, 60,
-                      false, false, true, decoder)) {
+                      false, false, true, decoder, 0)) {
         isHardwareAccelerated = decoder->isHardwareAccelerated();
         isFullScreenOnly = decoder->isAlwaysFullScreen();
         maxResolution = decoder->getDecoderMaxResolution();
@@ -432,7 +434,7 @@ void Session::getDecoderInfo(SDL_Window* window,
     // This will fall back to software decoding, so it should always work.
     if (chooseDecoder(StreamingPreferences::VDS_AUTO,
                       window, VIDEO_FORMAT_H264, 1920, 1080, 60,
-                      false, false, true, decoder)) {
+                      false, false, true, decoder, 0)) {
         isHardwareAccelerated = decoder->isHardwareAccelerated();
         isFullScreenOnly = decoder->isAlwaysFullScreen();
         maxResolution = decoder->getDecoderMaxResolution();
@@ -451,7 +453,7 @@ bool Session::isHardwareDecodeAvailable(SDL_Window* window,
 {
     IVideoDecoder* decoder;
 
-    if (!chooseDecoder(vds, window, videoFormat, width, height, frameRate, false, false, true, decoder)) {
+    if (!chooseDecoder(vds, window, videoFormat, width, height, frameRate, false, false, true, decoder, 0)) {
         return false;
     }
 
@@ -489,7 +491,7 @@ bool Session::populateDecoderProperties(SDL_Window* window)
                        m_StreamConfig.width,
                        m_StreamConfig.height,
                        m_StreamConfig.fps,
-                       false, false, true, decoder)) {
+                       false, false, true, decoder, 0)) {
         return false;
     }
 
@@ -1974,7 +1976,7 @@ void Session::execInternal()
                                    enableVsync,
                                    enableVsync && m_Preferences->framePacing,
                                    false,
-                                   s_ActiveSession->m_VideoDecoder)) {
+                                   s_ActiveSession->m_VideoDecoder, m_Preferences->minimumLatency)) {
                     SDL_AtomicUnlock(&m_DecoderLock);
                     SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
                                  "Failed to recreate decoder after reset");

app/streaming/session.h

@@ -101,7 +101,7 @@ class Session : public QObject
                        SDL_Window* window, int videoFormat, int width, int height,
                        int frameRate, bool enableVsync, bool enableFramePacing,
                        bool testOnly,
-                       IVideoDecoder*& chosenDecoder);
+                       IVideoDecoder*& chosenDecoder, int mimimumLatency);
 
     static
     void clStageStarting(int stage);

app/streaming/video/decoder.h

@@ -43,6 +43,7 @@ typedef struct _DECODER_PARAMETERS {
     bool enableVsync;
     bool enableFramePacing;
     bool testOnly;
+    int minimumLatency;
 } DECODER_PARAMETERS, *PDECODER_PARAMETERS;
 
 class IVideoDecoder {