QMovie webp frame stutters

Question

I'm using QMovie to play a webp animation on a QLabal, the code like:

Foo::Foo() {
    movie_ = new QMovie("/path/to/my.webp", "", this);
    ui->label->setMovie(movie_);
}
void Foo::on_pushButton_clicked() {
    movie_->stop();
    movie_->start();
}

But when I play the animation, the frame stutters, like:

I try to extract the webp frames by using QImage::save, the code like:

QImageReader *reader = new QImageReader("/path/to/my.webp");
reader->setDecideFormatFromContent(true);
for (int i = 0; i < reader->imageCount(); ++i) {
    QImage image;
    reader->read(&image);
    image.save(QString("frame_%1.png").arg(i));
    reader->jumpToNextImage();
}

all the extracted frames are stutters too, like:

But when I extract frames by using google libwebp tool, there is no any problem.like:

// extract frame 9, not problem
webpmux.exe -get frame 9  -o "frame_9.webp"
// paly webp animation, there is no any problem
vwebp.exe /path/to/my.webp

Is it a Qt problem? both Qt 5.9.4(i'm using) and Qt latest version(i'm trying) has this problem.

Answer 1

It seems a Qt bug, the bug has reported on Qt version 5.9.1: WebP: animations don't respect alpha

Qt said the bug was solved on version 5.9.2, but the problems still exist even Qt 5.11.

there is the offical solution:

diff --git a/src/plugins/imageformats/webp/qwebphandler.cpp b/src/plugins/imageformats/webp/qwebphandler.cpp
index 5a0ae4a..ce90158 100644
--- a/src/plugins/imageformats/webp/qwebphandler.cpp
+++ b/src/plugins/imageformats/webp/qwebphandler.cpp
@@ -122,6 +122,8 @@ bool QWebpHandler::ensureScanned() const
                 that->m_bgColor = QColor::fromRgba(QRgb(WebPDemuxGetI(m_demuxer, WEBP_FF_BACKGROUND_COLOR)));

                 that->m_composited = new QImage(that->m_features.width, that->m_features.height, QImage::Format_ARGB32);
+                if (that->m_features.has_alpha)
+                    that->m_composited->fill(Qt::transparent);

                 // We do not reset device position since we have read in all data
                 m_scanState = ScanSuccess;
@@ -193,6 +195,8 @@ bool QWebpHandler::read(QImage *image)
     } else {
         // Animation
         QPainter painter(m_composited);
+        if (m_features.has_alpha && m_iter.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND)
+            m_composited->fill(Qt::transparent);
         painter.drawImage(currentImageRect(), frame);

         *image = *m_composited;

Here is my solution:

1.add some code

// ${QT_SRC}/qtimageformats/src/plugins/imageformats/webp/qwebphandler.cpp
// function QWebpHandler::read
if (m_features.has_alpha && (m_iter.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND || 
            m_iter.blend_method == WEBP_MUX_NO_BLEND)) {
      m_composited->fill(Qt::transparent);
}

2. rebuild qt webp plugin

nmake module-qtimageformats

3. replace qwebp.dll

mv ${QT_DIR}/plugins/imageformats/qwebpd.dll ${QT_DIR}/plugins/imageformats/qwebpd.dll.bak

cp ${REBUILD_WEBP_PLUGINS} ${QT_DIR}/plugins/imageformats/qwebpd.dll