diff --git a/ffmpeg/audiodisplay.cc b/ffmpeg/audiodisplay.cc
index 0a4b321..c4844b4 100644
--- a/ffmpeg/audiodisplay.cc
+++ b/ffmpeg/audiodisplay.cc
@@ -106,7 +106,7 @@ void AudioDisplay::runDecoder()
             continue;
         }
         auto emitPosition = qScopeGuard([=]() { emit positionChanged(pts); });
-        if (!Clock::adjustDelay(delay)) {
+        if (!d_ptr->clock->adjustDelay(delay)) {
             qDebug() << "Audio Delay: " << delay;
             dropNum++;
             continue;
diff --git a/ffmpeg/clock.cc b/ffmpeg/clock.cc
index dc4795a..cac20e1 100644
--- a/ffmpeg/clock.cc
+++ b/ffmpeg/clock.cc
@@ -145,6 +145,11 @@ auto Clock::adjustDelay(qint64 &delay) -> bool
     if (speed() > 1.0 && delay < 0) {
         return false;
     } else if (delay < -Clock::ClockPrivate::s_diffThreshold) {
+        reset(pts()); // 有可能是因为网络下载过慢导致的延迟，需要重置
+        if (this == Clock::ClockPrivate::s_clock) { // 主时钟不丢帧
+            delay = 0;
+            return true;
+        }
         return false;
     } else if (qAbs(delay) <= Clock::ClockPrivate::s_diffThreshold) {
         delay = 0;
diff --git a/ffmpeg/clock.hpp b/ffmpeg/clock.hpp
index 5be3f7e..3b36100 100644
--- a/ffmpeg/clock.hpp
+++ b/ffmpeg/clock.hpp
@@ -32,7 +32,7 @@ class Clock : public QObject
     auto getDelayWithMaster(qint64 &delay) const -> bool;
 
     // return true if delay is valid
-    static auto adjustDelay(qint64 &delay) -> bool;
+    auto adjustDelay(qint64 &delay) -> bool;
 
     static void globalSerialRef();
     static void globalSerialReset();
diff --git a/ffmpeg/subtitledisplay.cc b/ffmpeg/subtitledisplay.cc
index 982d951..dd83f1a 100644
--- a/ffmpeg/subtitledisplay.cc
+++ b/ffmpeg/subtitledisplay.cc
@@ -129,12 +129,12 @@ void SubtitleDisplay::runDecoder()
             continue;
         }
         auto delayDuration = delay + subtitlePtr->duration();
-        if (!Clock::adjustDelay(delayDuration)) {
+        if (!d_ptr->clock->adjustDelay(delayDuration)) {
             qDebug() << "Subtitle Delay: " << delay;
             dropNum++;
             continue;
         }
-        if (Clock::adjustDelay(delay)) {
+        if (d_ptr->clock->adjustDelay(delay)) {
             if (delay > 0) {
                 QMutexLocker locker(&d_ptr->mutex);
                 d_ptr->waitCondition.wait(&d_ptr->mutex, delay / 1000);
diff --git a/ffmpeg/videodisplay.cc b/ffmpeg/videodisplay.cc
index e5d65bd..77fea2e 100644
--- a/ffmpeg/videodisplay.cc
+++ b/ffmpeg/videodisplay.cc
@@ -111,7 +111,7 @@ void VideoDisplay::runDecoder()
             continue;
         }
         auto emitPosition = qScopeGuard([=]() { emit positionChanged(pts); });
-        if (!Clock::adjustDelay(delay)) {
+        if (!d_ptr->clock->adjustDelay(delay)) {
             qDebug() << "Video Delay: " << delay;
             dropNum++;
             continue;
diff --git a/ffmpeg/videorender/openglrender.cc b/ffmpeg/videorender/openglrender.cc
index 5174e79..67c4f22 100644
--- a/ffmpeg/videorender/openglrender.cc
+++ b/ffmpeg/videorender/openglrender.cc
@@ -200,23 +200,6 @@ void OpenglRender::initSubTexture()
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 }
 
-void OpenglRender::resizeViewport()
-{
-    auto avframe = d_ptr->framePtr->avFrame();
-    auto size = QSize(avframe->width, avframe->height);
-    size.scale(this->size(), Qt::KeepAspectRatio);
-    auto rect = QRectF((width() - size.width()) / 2.0,
-                       (height() - size.height()) / 2.0,
-                       size.width(),
-                       size.height());
-    // 设置视图大小实现图片自适应
-    auto devicePixelRatio = this->devicePixelRatio();
-    glViewport(rect.x() * devicePixelRatio,
-               rect.y() * devicePixelRatio,
-               rect.width() * devicePixelRatio,
-               rect.height() * devicePixelRatio);
-}
-
 void OpenglRender::setColorSpace()
 {
     auto avFrame = d_ptr->framePtr->avFrame();
@@ -239,9 +222,21 @@ void OpenglRender::setColorSpace()
     }
 }
 
+auto OpenglRender::fitToScreen(const QSize &size) -> QMatrix4x4
+{
+    auto factor_w = qreal(width()) / size.width();
+    auto factor_h = qreal(height()) / size.height();
+    auto factor = qMin(factor_w, factor_h);
+    QMatrix4x4 matrix;
+    matrix.setToIdentity();
+    matrix.scale(factor / factor_w, factor / factor_h);
+    return matrix;
+}
+
 void OpenglRender::paintVideoFrame()
 {
-    auto format = d_ptr->framePtr->avFrame()->format;
+    auto avFrame = d_ptr->framePtr->avFrame();
+    auto format = avFrame->format;
     //qDebug() << format;
     // 绑定纹理
     switch (format) {
@@ -272,7 +267,7 @@ void OpenglRender::paintVideoFrame()
     }
     d_ptr->programPtr->bind(); // 绑定着色器
     d_ptr->programPtr->setUniformValue("format", format);
-
+    d_ptr->programPtr->setUniformValue("transform", fitToScreen({avFrame->width, avFrame->height}));
     setColorSpace();
     draw();
     d_ptr->programPtr->release();
@@ -302,6 +297,7 @@ void OpenglRender::paintSubTitleFrame()
                  img.constBits());
     glEnable(GL_BLEND);
     d_ptr->subProgramPtr->bind();
+    d_ptr->subProgramPtr->setUniformValue("transform", fitToScreen(img.size()));
     draw();
     d_ptr->subProgramPtr->release();
     glDisable(GL_BLEND);
@@ -366,6 +362,12 @@ void OpenglRender::initializeGL()
     glBindVertexArray(0); // 设置为零以破坏现有的顶点数组对象绑定}
 }
 
+void OpenglRender::resizeGL(int w, int h)
+{
+    auto ratioF = devicePixelRatioF();
+    glViewport(0, 0, w * ratioF, w * ratioF);
+}
+
 void OpenglRender::paintGL()
 {
     clear();
@@ -374,8 +376,6 @@ void OpenglRender::paintGL()
         return;
     }
 
-    resizeViewport();
-
     paintVideoFrame();
     paintSubTitleFrame();
 }
diff --git a/ffmpeg/videorender/openglrender.hpp b/ffmpeg/videorender/openglrender.hpp
index 673de5b..b3f7b42 100644
--- a/ffmpeg/videorender/openglrender.hpp
+++ b/ffmpeg/videorender/openglrender.hpp
@@ -28,6 +28,7 @@ class FFMPEG_EXPORT OpenglRender : public VideoRender,
 
 protected:
     void initializeGL() override;
+    void resizeGL(int w, int h) override;
     void paintGL() override;
 
     void updateFrame(QSharedPointer<Frame> frame) override;
@@ -38,8 +39,8 @@ class FFMPEG_EXPORT OpenglRender : public VideoRender,
     void draw();
     void initTexture();
     void initSubTexture();
-    void resizeViewport();
     void setColorSpace();
+    auto fitToScreen(const QSize &size) -> QMatrix4x4;
 
     void paintVideoFrame();
     void paintSubTitleFrame();
diff --git a/ffmpeg/videorender/shader/video.vert b/ffmpeg/videorender/shader/video.vert
index c9c6918..78d847d 100644
--- a/ffmpeg/videorender/shader/video.vert
+++ b/ffmpeg/videorender/shader/video.vert
@@ -1,10 +1,13 @@
 #version 330 core
+
 layout(location = 0) in vec3 aPos;
 layout(location = 1) in vec2 aTexCord;
 out vec2 TexCord; // 纹理坐标
 
+uniform mat4 transform;
+
 void main()
 {
-    gl_Position = vec4(aPos.x, -aPos.y, aPos.z, 1.0); // 图像坐标和OpenGL坐标Y轴相反，
-    TexCord = aTexCord;
+    gl_Position = transform * vec4(aPos, 1.0);
+    TexCord = vec2(aTexCord.x, 1.0 - aTexCord.y);
 }