fix seek relative -5s，-10s；

README.md

@@ -13,6 +13,16 @@
 2. 在WidgetRender中，尽可能使用QImage::Format_RGB32和QImage::Format_ARGB32_Premultiplied图像格式。如下原因：
    1. Avoid most rendering directly to most of these formats using QPainter. Rendering is best optimized to the Format_RGB32  and Format_ARGB32_Premultiplied formats, and secondarily for rendering to the Format_RGB16, Format_RGBX8888,  Format_RGBA8888_Premultiplied, Format_RGBX64 and Format_RGBA64_Premultiplied formats.
 
+### ``avformat_seek_file``，当seek的时间点小于当前时间点一些时，比如-5秒、-10秒，seek不到目标时间点
+
+#### 有一种解决方法是：先``seek``到0秒，再``seek``到目标时间点。  
+这个时候-5秒、-10秒的seek，效果非常好，比之前好很多，之前有时候会卡在当前时间点，无法seek到目标时间点。
+
+```C++
+formatCtx->seek(0);
+formatCtx->seek(position);
+```
+
 ### Ffmpeg（5.0）在解码字幕与4.4.3不太一样
 
 ### 解码字幕(ffmpeg-n5.0):

examples/player/mainwindow.cpp

@@ -87,7 +87,6 @@ class MainWindow::MainWindowPrivate
             playerPtr->addEvent(eventPtr);
         });
         new QShortcut(QKeySequence::MoveToPreviousChar, q_ptr, q_ptr, [this] {
-            // Todo : seek 不准确
             Ffmpeg::EventPtr eventPtr(new Ffmpeg::SeekRelativeEvent(-5));
             playerPtr->addEvent(eventPtr);
         });

ffmpeg/player.cpp

@@ -347,7 +347,9 @@ class Player::PlayerPrivate
         subtitleDecoder->addEvent(eventPtr);
         auto position = seekEvent->position();
         seekEvent->wait();
-
+        // before add this line, seek position less than current position, it wiil not accurate,
+        // and now first seek to 0, then seek to position, it will be very good
+        formatCtx->seek(0);
         formatCtx->seek(position);
         if (audioInfo->isIndexVaild()) {
             audioInfo->codecCtx()->flush();