MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

msInsertVideoEffect
msInsertAudioEffect
msClearEffects
msSetMediaProtectionManager
msSetVideoRectangle
onMSVideoFrameStepCompleted (event)
Adds or removes effects during playback (see below). All are available on video;
msInsertVideoEffect is not available on audio elements.
Used for DRM with both audio and video; see “Streaming from a Server and Digital Rights
Management (DRM)” toward the end of this chapter.
Sets the dimension of a subrectangle within a video.
Occurs when the video format changes.
The Source Attribute and Custom Codecs
Video (and audio) elements can use the HTML5 source attribute. In web applications, multiple
source elements are used to provide alternate video formats in case a client system doesn’t have
the necessary codec for the primary source. Given that the list of supported formats in Windows is
well known (refer again to Supported audio and video formats), this isn’t much of a concern for
Windows Store apps. However, source is still useful because it can identify the specific codecs for
the source:
This is important when you need to provide a custom codec for your app through
Windows.Media.MediaExtensionManager, outlined in the “Custom Decoders/Encovers and Scheme
Handlers” section later in this chapter, as the codec identifies the extension to load for decoding. I
show WebM as an example here because it’s not directly available to Store apps (though it is in
Internet Explorer). When the app host running a Store app encounters the video element above, it
will look for a matching decoder for the specified type.
Applying a Video Effect
The earlier table shows that video elements have msInsertVideoEffect and msInsertAudio-Effect
methods on them. WinRT provides a built-in video stabilization effect that is easily applied to an
element. This is demonstrated in Scenario 3 of the Media extensions sample, which plays the same video
with and without the effect, so the stabilized one is muted:
vidStab.msClearEffects();
vidStab.muted = true;
vidStab.msInsertVideoEffect(Windows.Media.VideoEffects.videoStabilization, true, null);
Custom effects, as demonstrated in Scenario 4 of the sample, are implemented as separate
dynamic-link libraries (DLLs), typically written in C++ for best performance, and are included in the app
package because a Store app can install a DLL only for its own use and not for systemwide access. With
the sample you’ll find DLL projects for a grayscale, invert, and geometric effects, where the latter has
three options for fisheye, pinch, and warp. In the js/CustomEffect.js file you can see how these are
applied, with the first parameter to msInsertVideoEffect being a string that identifies the effect as
exported by the DLL (see, for instance, the InvertTransform.idl file in the InvertTransform project):
420