使用Windows Graphics Capture API暂停/恢复屏幕录制

Question

我正在使用Windows Graphics Capture API在c#中构建一个屏幕记录应用程序。我正在使用这个脚本。我可以选择监视器，可以录制到mp4文件。我正在尝试添加暂停/恢复功能。

下面是主窗口的代码启动录音

try
{
newFile = GetTempFile();
using (var stream = new FileStream(newFile, FileMode.CreateNew).AsRandomAccessStream())
using (_encoder = new Encoder(_device, item))
{
await _encoder.EncodeAsync(
stream,
width, height, bitrate,
frameRate);
}
}
catch (Exception ex)
{
//
}

下面是编码器类的主要函数，

上面使用

private async Task EncodeInternalAsync(IRandomAccessStream stream, uint width, uint height, uint bitrateInBps, uint frameRate)
{
if (!_isRecording)
{
_isRecording = true;
_frameGenerator = new CaptureFrameWait(
_device,
_captureItem,
_captureItem.Size);
using (_frameGenerator)
{
var encodingProfile = new MediaEncodingProfile();
encodingProfile.Container.Subtype = "MPEG4";
encodingProfile.Video.Subtype = "H264";
encodingProfile.Video.Width = width;
encodingProfile.Video.Height = height;
encodingProfile.Video.Bitrate = bitrateInBps;
encodingProfile.Video.FrameRate.Numerator = frameRate;
encodingProfile.Video.FrameRate.Denominator = 1;
encodingProfile.Video.PixelAspectRatio.Numerator = 1;
encodingProfile.Video.PixelAspectRatio.Denominator = 1;
var transcode = await _transcoder.PrepareMediaStreamSourceTranscodeAsync(_mediaStreamSource, stream, encodingProfile);
await transcode.TranscodeAsync();
}
}
}

最后这是中的初始化函数CaptureFrameWait类

private void InitializeCapture(SizeInt32 size)
{
_framePool = Direct3D11CaptureFramePool.CreateFreeThreaded(
_device,
DirectXPixelFormat.B8G8R8A8UIntNormalized,
1,
size);
_framePool.FrameArrived += OnFrameArrived;
_session = _framePool.CreateCaptureSession(_item);
_session.IsBorderRequired = false;
_session.StartCapture();
}

我们如何修改它来暂停录制?我试图处理_framepool和_session在CaptureFrameWait中暂停并在恢复时重新初始化它们类，如下所示。它工作得很好，但有时TranscodeAsync函数在暂停期间终止并结束记录。我们怎样才能避免这种情况呢?

bool _paused = false;
public void PauseSession(bool status)
{
if (status) {
_paused = true;
_framePool?.Dispose();
_session?.Dispose();
}
else {
InitializeCapture(_size);
_paused = false;
}
}

Answer 1

解决方案之一是获得延期。医生说:

MediaStreamSource将等待您提供MediaStreamSample，直到您将延迟标记为完成。

例如，为Encoder类添加两个私有成员和两个方法:

private MediaStreamSourceSampleRequestedEventArgs _args;
private MediaStreamSourceSampleRequestDeferral _def;
public bool IsPaused { get; private set; }
public void Pause()
{
IsPaused = true;
}
public void Resume()
{
IsPaused = false;
// complete the request we saved earlier
OnMediaStreamSourceSampleRequested(_mediaStreamSource, _args);
}

并像这样修改OnMediaStreamSourceSampleRequested方法(在我放置注释的地方):

private void OnMediaStreamSourceSampleRequested(MediaStreamSource sender, MediaStreamSourceSampleRequestedEventArgs args)
{
if (_isRecording && !_closed)
{
// if paused get a deferral and save the current arguments.
// OnMediaStreamSourceSampleRequested will not be called again until we complete the deferral
if (IsPaused)
{
_def = args.Request.GetDeferral();
_args = args;
return;
}
try
{
using (var frame = _frameGenerator.WaitForNewFrame())
{
if (frame == null)
{
args.Request.Sample = null;
DisposeInternal();
return;
}
var timeStamp = frame.SystemRelativeTime;
var sample = MediaStreamSample.CreateFromDirect3D11Surface(frame.Surface, timeStamp);
args.Request.Sample = sample;
// when called again (manually by us) complete the work
// and reset members
if (_def != null)
{
_def.Complete();
_def = null;
_args = null;
}
}
}
catch (Exception e)
{
...
}
}
else
{
...
}
}

另一个解决方案是简单地冻结帧的时间戳，因此添加这些成员:

private TimeSpan _pausedTimestamp;
public bool IsPaused { get; private set; }
public void Pause()
{
IsPaused = true;
}
public void Resume()
{
IsPaused = false;
}

并像这样修改OnMediaStreamSourceSampleRequested方法(我已经放了注释):

private void OnMediaStreamSourceSampleRequested(MediaStreamSource sender, MediaStreamSourceSampleRequestedEventArgs args)
{
if (_isRecording && !_closed)
{
try
{
using (var frame = _frameGenerator.WaitForNewFrame())
{
if (frame == null)
{
args.Request.Sample = null;
DisposeInternal();
return;
}
// if paused, "freeze" the timestamp
TimeSpan timeStamp;
if (IsPaused)
{
timeStamp = _pausedTimestamp;
}
else
{
timeStamp = frame.SystemRelativeTime;
_pausedTimestamp = timeStamp;
}
var sample = MediaStreamSample.CreateFromDirect3D11Surface(frame.Surface, timeStamp);
args.Request.Sample = sample;
}
}
catch (Exception e)
{
...
}
}
else
{
...
}
}