摘要：在前两篇Silverlight的文章中跟大家一块学习了Silverlight的基础知识、Silverlight摄像头麦克风的相关操作以及截图、声音录制等，在文章后面也简单的说明了为什么没有视频录制，今天就和大家一块看一下上一节中最后的一个问题：如何使用Silverlight进行视频录制。
主要内容：
1.NESL项目简介
2.使用NESL实现视频录制
3.注意
一、NESL项目简介
在silverlight 中如何录制视频？相信这个问题有不少朋友都搜索过，但是好像目前还没有见到很好的答案，究其原因其实就是视频编码问题。当然也有朋友提到直接进行截图，只要每秒截取足够多的图片，然后依次播放就可以形成视频。但是我看到国外一个朋友使用此方法进行了几十秒的视频录制，其文件大小就达到了百兆级别，而且还进行了优化。因此这种方式要实现视频录制就目前而言还不是很合适。那么到底有没有好的方法呢？答案是有，但有限制，那就是借助于NESL。
Native Extensions for Silverlight（简称NESL）是由微软Silverlight团队进行开发，其目的主要为了增强Silverlight Out-of-Browser离线应用的功能。大家都知道虽然Silverlight 4的OOB应用支持信任*限提升功能，允许Silverlight的OOB应用对COM组件的访问，但对绝大多数Windows API仍旧无法调用，而NESL的出现正是为了解决这个问题。在最新的NESL 2.0中包含了大量有用的功能，而这其中就包括今天要说的视频编码部分。在NESL中有一个类库Microsoft.Silverlight.Windows.LocalEncode.dll主要负责本地视频和音频编码，这里就是用此类库来解决上面提到的视频录制问题。
二、使用NESL实现视频录制
在Microsoft.Silverlight.Windows.LocalEncode.dll中一个核心类就是EncodeSession，它负责音频和视频的编码输出工作。使用EncodeSession进行视频录制大概分为下面两步：
1.准备输入输出信息
在这个过程中需要定义VideInputFormatInfo、AudioInputFormatInfo、VideoOutputFormatInfo、AudioOutputFormatInfo和OutputContainerInfo，然后调用EncodeSession.Prepare()方法。
2.捕获视频输出
当输入输出信息准备好之后接下来就是调用EncodeSession.Start()方法进行视频编码输出。当然为了接收音频和视频数据必须准备两个sink类，分别继承于AudioSink和VideoSink，在这两个sink中指定CaptureSource，并且在对应的OnSample中调用EncodeSession的WirteVideoSample()和WirteAudioSample()接收并编码数据（关于AudioSink在前面的文章中已经说过，VideoSink与之类似）。
知道了EncodeSession的使用方法后下面就将其操作进行简单封装，LocalCamera.cs是本例中的核心类：
using System;
using System.Collections.ObjectModel;
using System.IO;
using System.Windows;
using System.Windows.Threading;
using System.Windows.Media;
using System.Windows.Controls;
using System.Windows.Shapes;
using Microsoft.Silverlight.Windows.LocalEncode;
namespace Cmj.MyWeb.MySilverlight.SilverlightMeida
{ /// <summary>
/// 编码状态
/// </summary>
public enum EncodeSessionState
{
Start,
Pause,
Stop
}
/// <summary>
/// 本地视频对象
/// </summary>
public class LocalCamera
{
private string _saveFullPath = "";
private uint _videoWidth = 640;
private uint _videoHeight = 480;
private VideoSinkExtensions _videoSink = null;
private AudioSinkExtensions _audioSink= null;
private EncodeSession _encodeSession = null;
private UserControl _page = null;
private CaptureSource _cSource = null;
public LocalCamera(UserControl page,VideoFormat videoFormat,AudioFormat audioFormat)
{
//this._saveFullPath = saveFullPath;
this._videoWidth = (uint)videoFormat.PixelWidth;
this._videoHeight = (uint)videoFormat.PixelHeight;
this._page = page;
this.SessionState = EncodeSessionState.Stop;
//this._encodeSession = new EncodeSession();
_cSource = new CaptureSource();
this.VideoDevice = DefaultVideoDevice;
this.VideoDevice.DesiredFormat = videoFormat;
this.AudioDevice = DefaultAudioDevice;
this.AudioDevice.DesiredFormat = audioFormat;
_cSource.VideoCaptureDevice = this.VideoDevice;
_cSource.AudioCaptureDevice = this.AudioDevice;
audioInputFormatInfo = new AudioInputFormatInfo() { SourceCompressionType = FormatConstants.AudioFormat_PCM };
videoInputFormatInfo = new VideoInputFormatInfo() { SourceCompressionType = FormatConstants.VideoFormat_ARGB32 };
audioOutputFormatInfo = new AudioOutputFormatInfo() { TargetCompressionType = FormatConstants.AudioFormat_AAC };
videoOutputFormatInfo = new VideoOutputFormatInfo() { TargetCompressionType = FormatConstants.VideoFormat_H264 };
outputContainerInfo = new OutputContainerInfo() { ContainerType = FormatConstants.TranscodeContainerType_MPEG4 };
}
public LocalCamera(UserControl page,VideoCaptureDevice videoCaptureDevice,AudioCaptureDevice audioCaptureDevice, VideoFormat videoFormat, AudioFormat audioFormat)
{
//this._saveFullPath = saveFullPath;
this._videoWidth = (uint)videoFormat.PixelWidth;
this._videoHeight = (uint)videoFormat.PixelHeight;
this._page = page;
this.SessionState = EncodeSessionState.Stop;
//this._encodeSession = new EncodeSession();
_cSource = new CaptureSource();
this.VideoDevice = videoCaptureDevice;
this.VideoDevice.DesiredFormat = videoFormat;
this.AudioDevice = audioCaptureDevice;
this.AudioDevice.DesiredFormat = audioFormat;
_cSource.VideoCaptureDevice = this.VideoDevice;
_cSource.AudioCaptureDevice = this.AudioDevice;
audioInputFormatInfo = new AudioInputFormatInfo() { SourceCompressionType = FormatConstants.AudioFormat_PCM };
videoInputFormatInfo = new VideoInputFormatInfo() { SourceCompressionType = FormatConstants.VideoFormat_ARGB32 };
audioOutputFormatInfo = new AudioOutputFormatInfo() { TargetCompressionType = FormatConstants.AudioFormat_AAC };
videoOutputFormatInfo = new VideoOutputFormatInfo() { TargetCompressionType = FormatConstants.VideoFormat_H264 };
outputContainerInfo = new OutputContainerInfo() { ContainerType = FormatConstants.TranscodeContainerType_MPEG4 };
}
public EncodeSessionState SessionState
{
get;
set;
}
public EncodeSession Session
{
get
{
return _encodeSession;
}
set
{
_encodeSession = value;
}
}
/// <summary>
/// 编码对象所在用户控件对象
/// </summary>
public UserControl OwnPage
{
get
{
return _page;
}
set
{
_page = value;
}
}
/// <summary>
/// 捕获源
/// </summary>
public CaptureSource Source
{
get
{
return _cSource;
}
}
/// <summary>
/// 操作音频对象
/// </summary>
public AudioSinkExtensions AudioSink
{
get
{
return _audioSink;
}
}
public static VideoCaptureDevice DefaultVideoDevice
{
get
{
return CaptureDeviceConfiguration.GetDefaultVideoCaptureDevice();
}
}
public static ReadOnlyCollection<VideoCaptureDevice> AvailableVideoDevice
{
get
{
return CaptureDeviceConfiguration.GetAvailableVideoCaptureDevices();
}
}
public VideoCaptureDevice VideoDevice
{
get;
set;
}
public static AudioCaptureDevice DefaultAudioDevice
{
get
{
return CaptureDeviceConfiguration.GetDefaultAudioCaptureDevice();
}
}
public static ReadOnlyCollection<AudioCaptureDevice> AvailableAudioDevice
{
get
{
return CaptureDeviceConfiguration.GetAvailableAudioCaptureDevices();
}
}
public AudioCaptureDevice AudioDevice
{
get;
set;
}
private Object lockObj = new object();
internal VideoInputFormatInfo videoInputFormatInfo;
internal AudioInputFormatInfo audioInputFormatInfo;
internal VideoOutputFormatInfo videoOutputFormatInfo;
internal AudioOutputFormatInfo audioOutputFormatInfo;
internal OutputContainerInfo outputContainerInfo;
/// <summary>
/// 视频录制
/// </summary>
public void StartRecord()
{
lock (lockObj)
{
if (this.SessionState == EncodeSessionState.Stop)
{
_videoSink = new VideoSinkExtensions(this);
_audioSink = new AudioSinkExtensions(this);
//_audioSink.VolumnChange += new AudioSinkExtensions.VolumnChangeHanlder(_audioSink_VolumnChange);
if (_encodeSession == null)
{
_encodeSession = new EncodeSession();
}
PrepareFormatInfo(_cSource.VideoCaptureDevice.DesiredFormat, _cSource.AudioCaptureDevice.DesiredFormat);
_encodeSession.Prepare(videoInputFormatInfo, audioInputFormatInfo, videoOutputFormatInfo, audioOutputFormatInfo, outputContainerInfo);
_encodeSession.Start(false, 200);
this.SessionState = EncodeSessionState.Start;
}
}
}
/// <summary>
/// 音量大小指示
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
//void _audioSink_VolumnChange(object sender, VolumnChangeArgs e)
//{
// this.OwnPage.Dispatcher.BeginInvoke(new Action(() =>
// {
// (
// this.OwnPage.Tag as ProgressBar).Value = e.Volumn;
// }));
//}
/// <summary>
/// 暂停录制
/// </summary>
public void PauseRecord()
{
lock (lockObj)
{
this.SessionState = EncodeSessionState.Pause;
_encodeSession.Pause();
}
}
/// <summary>
/// 停止录制
/// </summary>
public void StopRecord()
{
lock (lockObj)
{
this.SessionState = EncodeSessionState.Stop;
_encodeSession.Shutdown();
_videoSink = null;
_audioSink = null;
}
}
/// <summary>
/// 准备编码信息
/// </summary>
/// <param name="videoFormat"></param>
/// <param name="audioFormat"></param>
private void PrepareFormatInfo(VideoFormat videoFormat, AudioFormat audioFormat)
{
uint FrameRateRatioNumerator = 0;
uint FrameRateRationDenominator = 0;
FormatConstants.FrameRateToRatio((float)Math.Round(videoFormat.FramesPerSecond, 2), ref FrameRateRatioNumerator, ref FrameRateRationDenominator);
videoInputFormatInfo.FrameRateRatioNumerator = FrameRateRatioNumerator;
videoInputFormatInfo.FrameRateRatioDenominator = FrameRateRationDenominator;
videoInputFormatInfo.FrameWidthInPixels = _videoWidth;
videoInputFormatInfo.FrameHeightInPixels = _videoHeight ;
videoInputFormatInfo.Stride = (int)_videoWidth*-4;
videoOutputFormatInfo.FrameRateRatioNumerator = FrameRateRatioNumerator;
videoOutputFormatInfo.FrameRateRatioDenominator = FrameRateRationDenominator;
videoOutputFormatInfo.FrameWidthInPixels = videoOutputFormatInfo.FrameWidthInPixels == 0 ? (uint)videoFormat.PixelWidth : videoOutputFormatInfo.FrameWidthInPixels;
videoOutputFormatInfo.FrameHeightInPixels = videoOutputFormatInfo.FrameHeightInPixels == 0 ? (uint)videoFormat.PixelHeight : videoOutputFormatInfo.FrameHeightInPixels;
audioInputFormatInfo.BitsPerSample = (uint)audioFormat.BitsPerSample;
audioInputFormatInfo.SamplesPerSecond = (uint)audioFormat.SamplesPerSecond;
audioInputFormatInfo.ChannelCount = (uint)audioFormat.Channels;
if (outputContainerInfo.FilePath == null || outputContainerInfo.FilePath == string.Empty)
{
_saveFullPath=System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyVideos), "cCameraRecordVideo.tmp");
}
outputContainerInfo.FilePath = _saveFullPath;
//outputContainerInfo.FilePath = _saveFullPath;
if (audioOutputFormatInfo.AverageBitrate == 0)
audioOutputFormatInfo.AverageBitrate = 24000;
if (videoOutputFormatInfo.AverageBitrate == 0)
videoOutputFormatInfo.AverageBitrate = 2000000;
}
/// <summary>
/// 开始捕获
/// </summary>
public void StartCaptrue()
{
if (CaptureDeviceConfiguration.AllowedDeviceAccess || CaptureDeviceConfiguration.RequestDeviceAccess())
{
_cSource.Start();
}
}
/// <summary>
/// 停止捕获
/// </summary>
public void StopCapture()
{
_videoSink = null;
_audioSink = null;
_cSource.Stop();
}
/// <summary>
/// 获得视频
/// </summary>
/// <returns></returns>
public VideoBrush GetVideoBrush()
{
VideoBrush vBrush = new VideoBrush();
vBrush.SetSource(_cSource);
return vBrush;
}
/// <summary>
/// 获得视频
/// </summary>
/// <returns></returns>
public Rectangle GetVideoRectangle()
{
Rectangle rctg = new Rectangle();
rctg.Width = this._videoWidth;
rctg.Height = this._videoHeight;
rctg.Fill = GetVideoBrush();
return rctg;
}
/// <summary>
/// 保存视频
/// </summary>
public void SaveRecord()
{
if (_saveFullPath == string.Empty)
{
MessageBox.Show("尚未录制视频，无法进行保存！", "系统提示", MessageBoxButton.OK);
return;
}
SaveFileDialog sfd = new SaveFileDialog
{
Filter = "MP4 Files (*.mp4)|*.mp4",
DefaultExt = ".mp4",
FilterIndex = 1
};
if ((bool)sfd.ShowDialog())
{
using (Stream stm=sfd.OpenFile())
{
FileStream fs = new FileStream(_saveFullPath, FileMode.Open, FileAccess.Read);
try
{
byte[] buffur = new byte[fs.Length];
fs.Read(buffur, 0, (int)fs.Length);
stm.Write(buffur, 0, (int)buffur.Length);
fs.Close();
File.Delete(_saveFullPath);
}
catch (IOException ioe)
{
MessageBox.Show("文件保存失败！错误信息如下："+Environment.NewLine+ioe.Message,"系统提示",MessageBoxButton.OK);
}
stm.Close();
}
}
}
}
} |
当然上面说过必须有两个Sink：
using System;
using System.Windows.Media;
using System.Windows.Controls;
using Microsoft.Silverlight.Windows.LocalEncode;
namespace Cmj.MyWeb.MySilverlight.SilverlightMeida
{ public class VideoSinkExtensions:VideoSink
{
//private UserControl _page;
//private EncodeSession _session;
private LocalCamera _localCamera;
public VideoSinkExtensions(LocalCamera localCamera)
{
//this._page = page;
this._localCamera = localCamera;
//this._session = session;
this.CaptureSource = _localCamera.Source;
}
protected override void OnCaptureStarted()
{
}
protected override void OnCaptureStopped()
{
}
protected override void OnFormatChange(VideoFormat videoFormat)
{
}
protected override void OnSample(long sampleTimeInHundredNanoseconds, long frameDurationInHundredNanoseconds, byte[] sampleData)
{
if (_localCamera.SessionState == EncodeSessionState.Start)
{
_localCamera.OwnPage.Dispatcher.BeginInvoke(new Action<long, long, byte[]>((ts, dur, data) =>
{
_localCamera.Session.WriteVideoSample(data, data.Length, ts, dur);
}), sampleTimeInHundredNanoseconds, frameDurationInHundredNanoseconds, sampleData);
}
}
}
} |
using System;
using System.Windows.Media;
using System.Windows.Controls;
using Microsoft.Silverlight.Windows.LocalEncode;
namespace Cmj.MyWeb.MySilverlight.SilverlightMeida
{ public class AudioSinkExtensions:AudioSink
{
private LocalCamera _localCamera;
public AudioSinkExtensions(LocalCamera localCamera)
{
this._localCamera = localCamera;
this.CaptureSource = _localCamera.Source;
}
protected override void OnCaptureStarted()
{
}
protected override void OnCaptureStopped()
{
}
protected override void OnFormatChange(AudioFormat audioFormat)
{
}
protected override void OnSamples(long sampleTimeInHundredNanoseconds, long sampleDurationInHundredNanoseconds, byte[] sampleData)
{
if (_localCamera.SessionState == EncodeSessionState.Start)
{
_localCamera.OwnPage.Dispatcher.BeginInvoke(new Action<long, long, byte[]>((ts, dur, data) =>
{
_localCamera.Session.WriteAudioSample(data, data.Length, ts, dur);
}), sampleTimeInHundredNanoseconds, sampleDurationInHundredNanoseconds, sampleData);
//计算音量变化
//for (int index = 0; index < sampleData.Length; index += 1)
//{
// short sample = (short)((sampleData[index] << 8) | sampleData[index]);
// float sample32 = sample / 32768f;
// float maxValue = 0;
// float minValue = 0;
// maxValue = Math.Max(maxValue, sample32);
// minValue = Math.Min(minValue, sample32);
// float lastPeak = Math.Max(maxValue, Math.Abs(minValue));
// float micLevel = (100 - (lastPeak * 100)) * 10;
// OnVolumnChange(this, new VolumnChangeArgs() { Volumn=micLevel});
//}
}
}
/// <summary>
/// 定义一个事件，反馈音量变化
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
//public delegate void VolumnChangeHanlder(object sender, VolumnChangeArgs e);
//public event VolumnChangeHanlder VolumnChange;
//private void OnVolumnChange(object sender, VolumnChangeArgs e)
//{
// if (VolumnChange != null)
// {
// VolumnChange(sender, e);
// }
//}
}
//public class VolumnChangeArgs : EventArgs
//{
// public float Volumn
// {
// get;
// internal set;
// }
//}
} |
有了这三个类，下面准备一个界面，使用LocalCamera进行视频录制操作。
需要注意的是保存操作，事实上在EncodeSession中视频的保存路径是在视频录制之前就必须指定的（当然这一点并不难理解，因为长时间的视频录制是会形成很大的文件的，保存之前缓存到内存中也不是很现实），在LocalCamera中对保存方法的封装事实上是文件的读取和删除操作。另外在这个例子中用到了前面文章中自定义的OOB控件，不明白的朋友可以查看前面的文章内容。下面是调用代码：
OK，下面是视频录制的截图：
正在录制
停止录制后保存
播放录制的视频
三、注意：
1.video sink和audio sink都是运行在不同于UI的各自的线程中，你可以使用UI的Dispathcher或者SynchronizationContext进行不同线程之间的调用。
2．在video sink和audio sink的OnSample方法中必须进行状态判断，因为sink实例创建之后就会执行OnSample方法，但此时EncodeSession还没有启动因此如果不进行状态判读就会抛出com异常。
3.视频的宽度和高度不能够随意指定，这个在NESL的帮助文档中也是特意说明的，如果任意指定同样会抛出异常。
4.最后再次提醒大家，上面的视频录制是基于NESL的因此必须将应用运行到浏览器外（OOB）。
源代码下载