windows media audio compressor - the code project - managed c++.mht

视频方面的资料

            =
href=3D"http://www.codeproject.com/managedcpp/WmaCompressor.asp#Figure =
2">figure=20
            2</A>, with no more added complexity. Unfortunately, there =
is no=20
            such managed WMF SDK, therefore, some tricks and wrapper =
classes are=20
            necessary to implement the compressor. If you are interested =
in=20
            knowing the details, you can look at <A=20
            =
href=3D"http://www.codeproject.com/managedcpp/WmaCompressor.asp#Figure =
3">figure=20
            3</A> in the <A=20
            =
href=3D"http://www.codeproject.com/managedcpp/WmaCompressor.asp#Implement=
ation details">implementation=20
            details</A> section of this article.</P>
            <H2>Using the code</H2>
            <P>Using the <CODE>WmaWriter</CODE> is easy. You can use it =
in the=20
            same way you use <CODE>BinaryWriter</CODE> =
(<CODE>WmaWriter</CODE>=20
            is a specialization of <CODE>BinaryWriter</CODE>: see <A=20
            =
href=3D"http://www.codeproject.com/managedcpp/WmaCompressor.asp#Figure =
2">figure=20
            2</A>). The only difference with <CODE>BinaryWriter</CODE> =
is that=20
            you must indicate at creation time the format of the input =
data=20
            (data that the writer will receive) using a =
<CODE>WaveFormat</CODE>=20
            instance, and a profile defining the settings of the =
resulting=20
            compressed stream.</P>
            <P>The following VB.NET code shows a simple way of =
compressing a WAV=20
            file using this compressor:</P><PRE lang=3Dvbnet><SPAN =
class=3Dvb-keyword>Imports</SPAN> Yeti.MMedia
<SPAN class=3Dvb-keyword>Imports</SPAN> Yeti.MMedia.Wmf
<SPAN class=3Dvb-keyword>Imports</SPAN> WaveLib
<SPAN class=3Dvb-keyword>Imports</SPAN> System.IO
....

  <SPAN class=3Dvb-keyword>Dim</SPAN> InStr <SPAN =
class=3Dvb-keyword>As</SPAN> WaveStream
  <SPAN class=3Dvb-keyword>Dim</SPAN> writer <SPAN =
class=3Dvb-keyword>As</SPAN> AudioWriter
  <SPAN class=3Dvb-keyword>Dim</SPAN> buff() <SPAN =
class=3Dvb-keyword>As</SPAN> <SPAN class=3Dvb-keyword>Byte</SPAN>
  <SPAN class=3Dvb-keyword>Dim</SPAN> read <SPAN =
class=3Dvb-keyword>As</SPAN> <SPAN class=3Dvb-keyword>Integer</SPAN>

  InStr =3D <SPAN class=3Dvb-keyword>New</SPAN> WaveStream(<SPAN =
class=3Dvb-string>"SomeFile.wav"</SPAN>)
  <SPAN class=3Dvb-keyword>Try</SPAN>
    writer =3D <SPAN class=3Dvb-keyword>New</SPAN> WmaWriter(<SPAN =
class=3Dvb-keyword>New</SPAN> FileStream(<SPAN =
class=3Dvb-string>"SomeFile.wma"</SPAN>, FileMode.Create), _
                          InStr.Format)
    <SPAN class=3Dvb-comment>'The previous line is equivalent to:</SPAN>
    <SPAN class=3Dvb-comment>'writer =3D New WmaWriter(New =
FileStream("SomeFile.wma", FileMode.Create), _</SPAN>
    <SPAN class=3Dvb-comment>'                       InStr.Format, =
_</SPAN>
    <SPAN class=3Dvb-comment>'                       =
WmaWriterProfileManager.AudioSystemProfiles(0))</SPAN>
    <SPAN class=3Dvb-keyword>Try</SPAN>
      buff =3D <SPAN class=3Dvb-keyword>New</SPAN> <SPAN =
class=3Dvb-keyword>Byte</SPAN>(writer.OptimalBufferSize - <SPAN =
class=3Dvb-literal>1</SPAN>) {}
      read =3D InStr.Read(buff, <SPAN class=3Dvb-literal>0</SPAN>, =
buff.Length)
      <SPAN class=3Dvb-keyword>While</SPAN> (read &gt; <SPAN =
class=3Dvb-literal>0</SPAN>)
        writer.Write(buff, <SPAN class=3Dvb-literal>0</SPAN>, read)
        read =3D InStr.Read(buff, <SPAN class=3Dvb-literal>0</SPAN>, =
buff.Length)
      <SPAN class=3Dvb-keyword>End</SPAN> <SPAN =
class=3Dvb-keyword>While</SPAN>
    <SPAN class=3Dvb-keyword>Finally</SPAN>
      writer.Close()
    <SPAN class=3Dvb-keyword>End</SPAN> <SPAN =
class=3Dvb-keyword>Try</SPAN>
  <SPAN class=3Dvb-keyword>Finally</SPAN>
    InStr.Close()
  <SPAN class=3Dvb-keyword>End</SPAN> <SPAN =
class=3Dvb-keyword>Try</SPAN></PRE>
            <P>I made the sample project in VB.NET just to please those =
who love=20
            VB. Anyway, you can use the compressor in C#, Managed C++, =
J# or any=20
            other CLS compliant language. The sample project of the MP3=20
            compressor (also included in the source files) is written in =
C#. You=20
            can also refer to my <A=20
            =
href=3D"http://www.codeproject.com/csharp/CSharpRipper.asp">C Sharp=20
            MP3 Compressor</A> article.</P>
            <P>Another example of using the writer could be an improved =
version=20
            of the ripper described in my article "<A=20
            =
href=3D"http://www.thecodeproject.com/csharp/CSharpRipper.asp">C Sharp=20
            Ripper</A>" to rip directly to WMA format. In the file=20
            <I>Form1.cs</I>, inside the handler of the "Save as.." =
button, there=20
            is the line:</P><PRE lang=3Dcs>m_Writer =3D <SPAN =
class=3Dcs-keyword>new</SPAN> WaveWriter(WaveFile, Format);</PRE>
            <P>Which may be changed to:</P><PRE lang=3Dcs>m_Writer =3D =
<SPAN class=3Dcs-keyword>new</SPAN> WmaWriter(WaveFile, Format);</PRE>
            <P>The rest of the code remains without change and, of =
course, if=20
            you need more control on the compressor parameters, then you =
should=20
            add extra code to supply a <CODE>WmaWriterProfile</CODE> =
instance in=20
            the constructor.</P>
            <H2><A name=3D"Implementation details">Implementation =
details</A></H2>
            <P>The figure below is a more complete class diagram of the=20
            compressor, showing the managed classes and interfaces and =
their=20
            relations with the WMF SDK interfaces.</P>
            <P><A=20
            =
href=3D"http://www.codeproject.com/managedcpp/WmaCompressor/ClassDiagram_=
big.jpg"=20
            target=3D_blank><IMG height=3D470=20
            =
src=3D"http://www.codeproject.com/managedcpp/WmaCompressor/ClassDiagram.j=
pg"=20
            width=3D600></A></P>
            <P><A name=3D"Figure 3">Figure 3</A>: Windows Media Audio =
Compressor:=20
            implementation details.</P>
            <P>I'm going to avoid the explanation of the implementation =
details.=20
            I just included the class diagram for those who want to see =
how this=20
            project was implemented and help them to better understand =
the code=20
            included with this article.</P>
            <P>If you only want to use the compressor as is, then you =
can safely=20
            ignore these implementation details.</P>
            <H2>Conclusion</H2>
            <P>As showed here, the use of this compressor is relatively =
easy=20
            even if the implementation is somewhat complex due to =
interaction of=20
            managed and unmanaged code. There are some features of =
Windows Media=20
            Format that are not included in this project, such as DRM =
support,=20
            metadata attributes and two-pass encoding.</P>
            <P>The sample code is given for demonstration purposes only, =
you can=20
            use it as reference if you need to develop some product with =
these=20
            technologies. When a managed version of WMF SDK is =
available, it=20
            will be easier to implement managed solutions using WMF. At =
the=20
            moment, this approach could be a good solution, considering =
that the=20
            unmanaged part can be suppressed without changing the design =
of=20
            managed part.</P><!-- Article Ends --></DIV></SPAN>
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