我开发了使用带有远程 url 的 MediaElement 播放视频的应用程序。一切正常，视频播放也很好。
但我面临的问题是，如果用户正在播放视频并且用户触摸了手机上的 windows 按钮。然后我的应用程序进入后台并显示主屏幕。现在在主屏幕上，用户触摸后退按钮。我的应用程序被带到前台，视频从头开始加载。无论如何我可以暂停 mediaelement 以便当用户回到我的应用程序时视频可以恢复。
还有一件事是我无法使用 MediaLauncher，因为我想在用户与媒体控件（例如播放/暂停）交互时记录一些事件。
请大家在这个场景中指导我。
谢谢。
【问题讨论】：
标签： windows-phone-8 windows-phone
您可以通过 ActivationPolicy 属性恢复您的应用程序到 DefaultTask 元素 inActivationPolicy 属性到 DefaultTask 元素在 WMAppManifest.xml 中并将值设置为“Resume”。对于此任务，您需要直接编辑应用清单，而不是使用清单编辑器。为此，请右键单击 WMAppManifest.xml，单击打开方式，然后选择 XML（文本）编辑器。
可以为 XAML 应用、Direct3D 应用和带有 XAML 应用的 Direct3D 启用 For Resume。以下示例显示 DefaultTask 元素将如何查找 XAML 应用和 Direct3D 应用。
<DefaultTask Name="_default" NavigationPage="MainPage.xaml" ActivationPolicy="Resume"/>
<DefaultTask Name="_default" ImagePath="PhoneDirect3DApp1.exe" ImageParams="" ActivationPolicy="Resume"/>
app resume for Windows Phone 8
如果这对您没有帮助，您可以像下面的代码一样手动播放并停止您的视频播放器
XAML
<Grid x:Name="LayoutRoot" Background="Transparent">
<Grid.RowDefinitions>
<RowDefinition Height="0.90*"/>
<RowDefinition Height="0.10*"/>
</Grid.RowDefinitions>
<SSME:SmoothStreamingMediaElement x:Name="video" Grid.Row="0" />
<!--TitlePanel contains the name of the application and page title-->
<StackPanel Orientation="Horizontal" Grid.Row="1">
<Button x:Name="PlayButton" Width="150" Click="PlayButton_Click" Loaded="PlayButton_Loaded"/>
<Button x:Name="StopButton" Content="Stop" Width="100" Click="StopButton_Click" />
<TextBlock x:Name="status"/>
<TextBlock x:Name="currentBitrate"/>
</StackPanel>
<!--ContentPanel - place additional content here-->
<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0"></Grid>
</Grid>
C# 代码：
public partial class VIdeoStraming : PhoneApplicationPage
{
string VideoUrl,StreamingUrl;
public VIdeoStraming()
{
InitializeComponent();
}
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
base.OnNavigatedTo(e);
VideoUrl = this.NavigationContext.QueryString["parameter0"];
string Manifest="/Manifest";
StreamingUrl = VideoUrl + Manifest;
}
private void PlayButton_Click(object sender, RoutedEventArgs e)
{
//Monitor the state of the content to determine the right action to take on this button being clicked
//and then change the text to reflect the next action
switch (video.CurrentState)
{
case SmoothStreamingMediaElementState.Playing:
video.Pause();
PlayButton.Content = "Play";
break;
case SmoothStreamingMediaElementState.Stopped:
case SmoothStreamingMediaElementState.Paused:
video.Play();
PlayButton.Content = "Pause";
break;
}
}
private void PlayButton_Loaded(object sender, RoutedEventArgs e)
{
switch (video.AutoPlay)
{
case false:
PlayButton.Content = "Play";
break;
case true:
PlayButton.Content = "Pause";
break;
}
}
private void StopButton_Click(object sender, RoutedEventArgs e)
{
//This should simply stop the playback
video.Stop();
//We should also reflect the chang on the play button
PlayButton.Content = "Play";
}
private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
{
video.CurrentStateChanged += new RoutedEventHandler(video_CurrentStateChanged);
video.PlaybackTrackChanged += new EventHandler<Microsoft.Web.Media.SmoothStreaming.TrackChangedEventArgs>(video_PlaybackTrackChanged);
//video.SmoothStreamingSource = new Uri("http://64.120.251.114:1945/live/sharedobjects/layoutvideo/mp4:1311370468970.MP4/Manifest");
video.SmoothStreamingSource = new Uri(StreamingUrl);
video.ManifestReady += new EventHandler<EventArgs>(video_ManifestReady);
}
//when use in mobile device
void video_ManifestReady(object sender, EventArgs e)
{
SmoothStreamingMediaElement ssme = sender as SmoothStreamingMediaElement;
if (ssme == null)
{
return;
}
// Select the highest band of tracks which all have the same resolution.
// maxMobileBitrate depends on the encoding settings
const ulong maxMobileBitrate = 1000000;
foreach (SegmentInfo segment in ssme.ManifestInfo.Segments)
{
foreach (StreamInfo streamInfo in segment.AvailableStreams)
{
if (MediaStreamType.Video == streamInfo.Type)
{
List<TrackInfo> widestBand = new List<TrackInfo>();
List<TrackInfo> currentBand = new List<TrackInfo>();
ulong lastHeight = 0;
ulong lastWidth = 0;
ulong index = 0;
foreach (TrackInfo track in streamInfo.AvailableTracks)
{
index += 1;
string strMaxWidth;
string strMaxHeight;
// If can't find width/height, choose only the top bitrate.
ulong ulMaxWidth = index;
// If can't find width/height, choose only the top bitrate.
ulong ulMaxHeight = index;
// V2 manifests require "MaxWidth", while v1 manifests used "Width".
if (track.Attributes.TryGetValue("MaxWidth", out strMaxWidth) ||
track.Attributes.TryGetValue("Width", out strMaxWidth))
{
ulong.TryParse(strMaxWidth, out ulMaxWidth);
}
if (track.Attributes.TryGetValue("MaxHeight", out strMaxHeight) ||
track.Attributes.TryGetValue("Height", out strMaxHeight))
{
ulong.TryParse(strMaxHeight, out ulMaxHeight);
}
if (ulMaxWidth != lastWidth ||
ulMaxHeight != lastHeight)
{
// Current band is now finished, check if it is the widest.
// If same size, current band preferred over previous
// widest, because it will be of higher bitrate.
if (currentBand.Count >= widestBand.Count)
{
// A new widest band:
widestBand = currentBand;
currentBand = new List<TrackInfo>();
}
}
if (track.Bitrate > maxMobileBitrate)
{
break;
}
// Current track always gets added to current band.
currentBand.Add(track);
lastWidth = ulMaxWidth;
lastHeight = ulMaxHeight;
}
if (0 == widestBand.Count &&
0 == currentBand.Count)
{
// Lowest bitrate band is > maxMobileBitrate.
widestBand.Add(streamInfo.AvailableTracks[0]);
}
else if (currentBand.Count >= widestBand.Count)
{
// Need to check the last band which was constructed.
Debug.Assert(currentBand.Count > 0);
widestBand = currentBand; // Winner by default.
}
Debug.Assert(widestBand.Count >= 1);
streamInfo.RestrictTracks(widestBand);
}
}
}
}
void video_PlaybackTrackChanged(object sender, Microsoft.Web.Media.SmoothStreaming.TrackChangedEventArgs e)
{
currentBitrate.Text = e.NewTrack.Bitrate.ToString();
}
void video_CurrentStateChanged(object sender, RoutedEventArgs e)
{
status.Text = video.CurrentState.ToString();
}
private void imghdrleft_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
NavigationService.GoBack();
}
private void imghdrright_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
NavigationService.Navigate(new Uri("/Planet41VIew/Settings.xaml", UriKind.RelativeOrAbsolute));
}
}
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