普通网站检测浏览器是否支持格式在webkit中的实现方式

最新推荐文章于 2022-05-07 14:17:41 发布

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最新推荐文章于 2022-05-07 14:17:41 发布

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分类专栏： WebKit内核系列 android系列文章标签： webkit 浏览器 string video html5 flash

本文链接：https://blog.youkuaiyun.com/lihui130135/article/details/7259023

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本文介绍了HTML5中video标签的canPlayType属性如何用于判断浏览器是否支持特定的媒体类型。通过WebKit源代码示例说明了canPlayType方法的具体实现过程。

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在优酷网站中如果对应某个属性不支持就会报出错误说不支持

在html5 video的使用过程中也是存在这样的问题

video标签包含一个

canPlayType属性，这个可以判断你浏览器内部是否支持某一属性。

对应到webkit的代码中就是：
String HTMLMediaElement::canPlayType(const String& mimeType) const
{
    MediaPlayer::SupportsType support = MediaPlayer::supportsType(ContentType(mimeType));
    String canPlay;

    // 4.8.10.3
    switch (support)
    {
        case MediaPlayer::IsNotSupported:
            canPlay = "";
            break;
        case MediaPlayer::MayBeSupported:
            canPlay = "maybe";
            break;
        case MediaPlayer::IsSupported:
            canPlay = "probably";
            break;
    }

    return canPlay;
}

根据webkit本身的语法规定是存在idl文件与之想对应

DOMString canPlayType(in DOMString type);

以下是具体的调用的backtrace：

#0 WebCore::MediaPlayerPrivate::supportsType (type=@0x4ef7c524, codecs=@0x4ef7c520) at external/webkit/WebKit/android/WebCoreSupport/MediaPlayerPrivateAndroid.cpp:547
#1 0xa83f9a40 in chooseBestEngineForTypeAndCodecs (type=<value optimized out>, codecs=<value optimized out>) at external/webkit/WebCore/platform/graphics/MediaPlayer.cpp:197
#2 0xa83f9cca in WebCore::MediaPlayer::supportsType (contentType={m_type = {m_impl = {<WTF::FastAllocBase> = {<No data fields>}, m_ptr = 0xa517b8}}})
at external/webkit/WebCore/platform/graphics/MediaPlayer.cpp:565
#3 0xa838c9dc in WebCore::HTMLMediaElement::canPlayType (this=<value optimized out>, mimeType=<value optimized out>) at external/webkit/WebCore/html/HTMLMediaElement.cpp:418
warning: (Internal error: pc 0xa85a660f in read in psymtab, but not in symtab.)
#4 0xa85a6610 in canPlayTypeCallback (args=<value optimized out>)
at out/debug/target/product/newbox/obj/STATIC_LIBRARIES/libwebcore_intermediates/WebCore/bindings/V8HTMLMediaElement.cpp:317
warning: (Internal error: pc 0xa85a660f in read in psymtab, but not in symtab.)
#5 0xa8610d96 in HandleApiCallHelper<false> (args={<v8::internal::Arguments> = {length_ = 3, arguments_ = 0x4ef7c60c}, <No data fields>}) at external/v8/src/builtins.cc:783
#6 0xa8610df0 in Builtin_HandleApiCall (args={<v8::internal::Arguments> = {length_ = 3, arguments_ = 0x4ef7c60c}, <No data fields>}) at external/v8/src/builtins.cc:800
#7 0x44a72234 in ?? ()

与此类似的flash的npnpi的方式也又对应的类型检查