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Posted 30 Jul 2002


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Converting Wav file to MP3 or other format using DirectShow

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30 Jul 2002CPOL3 min read
Simple class to convert stereo 44 kHz, 16 bit wav file to another format, including MP3. The class shows how to use DirectShow API for audio conversion.

Sample Image - DShowEncoder.gif


This article explains how to use the DirectShow API for simple audio conversion, particularly Wav to MP3 conversion. Audio codecs in the DirectShow API are of three type : native codecs, ACM codecs, and DMO (DirectX Media Object) codecs.

There are only few audio native codecs for audio compression. For MP3 encoding, the only one that I've found is the LAME DirectShow wrapper from Elecard. Most MP3 encoders are in the ACM (Audio Compression Manager) format, wich was introduced with the Windows Multimedia API. CDSEncoder class and it's relative classes CDSCodec and CDSCodecFormat enumerate ACM codecs and their respective compression parameters, construct a graph and do the encoding.

The GraphBuilder and other filters

Image 2

The graph consist of five filters:

  • File source (async) for reading the input wav file,
  • WAV Parser for wav parsing,
  • ACM codec for audio compression (in this case : MP3 ACM, wrapped by the ACM Wrapper Filter),
  • WAV Dest, for wav output multiplexing,
  • File Writer for writing the output file.

Important note

The WAV Dest filter is not included in standard filters, but need to be compiled from the DirectX SDK (SDK_root\Samples\Multimedia\DirectShow\Filters\WavDest). For convenience, the compiled WAV Dest filter is included in the demo zip, but you have to register it by RegSrv32

ACM codecs and the ACM Wrapper filter

All of the ACM codecs are listed in DirectShow in the Audio Compressors Filter Category (CLSID_AudioCompressorCategory) and cannot be instantiated directly. We have to use the Device Enumerator to use them.

Note : Depending of your configuration, several ACM codecs for a same format can be installed on your computer. This can be the case for MP3 codecs. You set priority or deactivate some of them by the use of control panel, as show in the following figure.

Codec configuration

The DeviceEnumerator or how to browse ACM codecs

The Device Enumerator must be used to retrieve an instance of an ACM codec. It returns the codecs list by the IEnumMoniker interface, so we can get the filter interface (IBaseFilter) by a call to IMoniker::BindToObject() and the filter name by a call to IMoniker::BindToStorage().

Configuring the ACM codec with IAMStreamConfig interface

Once the desired codec is instantiated, we can obtain an IBaseFilter interface for filter configuration. Since each IBaseFilter have one or more Pin, we have to search the output Pin by the use of the IEnumPins interface and IPin::QueryDirection() calls.
With the output Pin, we can query the IAMStreamConfig interface to configure the following property :

  • Numbers of channels,
  • Samples per second,
  • Average byte per second,
  • Bits per sample.

Note : For some codecs (including MP3), the call to IAMStreamConfig::SetFormat() must be after the graph rendering.

The classes


CDSEncoder assumes the following task :

  • Enumerate the Audio codecs (CLSID_AudioCompressorCategory),
  • Build, render, and run the graph.

class CDSEncoder : public CArray<CDSCodec*, CDSCodec*>
  void BuildGraph(CString szSrcFileName, CString szDestFileName, 
    int nCodec, int nFormat);
  virtual ~CDSEncoder();

  void BuildCodecArray();
  HRESULT AddFilterByClsid(IGraphBuilder *pGraph, LPCWSTR wszName, 
    const GUID& clsid, IBaseFilter **ppF);
  BOOL SetFilterFormat(AM_MEDIA_TYPE* pStreamFormat, 
    IBaseFilter* pBaseFilter);

  IGraphBuilder *m_pGraphBuilder;

As CDSEncoder inherits from CArray, the collection of codecs is exposed by CArray methods with each codecs returned as CDSCodec object.


CDSCodec assumes the following task :

  • Enumerate the codec supported parameters,
  • expose the codec name.

class CDSCodec : public CArray<CDSCodecFormat*, CDSCodecFormat*>
  virtual ~CDSCodec();

  CString m_szCodecName;
  IMoniker  *m_pMoniker;
  void BuildCodecFormatArray();

As CDSCodec inherits from CArray, the collection of codecs supported parameters is exposed by CArray methods with each parameters returned as CDSCodecFormat object.


CDSCodecFormat exposes the properties of one-codec parameters :

  • Number of channels,
  • Samples per second,
  • Bytes per second,
  • Bits per samples.

class CDSCodecFormat  
  WORD BitsPerSample();
  DWORD BytesPerSec();
  DWORD SamplesPerSecond();
  WORD NumberOfChannels();
  virtual ~CDSCodecFormat();

  AM_MEDIA_TYPE* m_pMediaType;

Known issues

Errors Checking

The article goal is to demonstrate the use of DirectShow for simple audio conversion. These classes are not as safe as they have to be. Please keep this in mind if you plan to use it in a production environment.

Source Wav format

There are no sampling conversion, so you can only generate 44 kHz output files if you use 44 kHz Wav.

Windows Media

Windows Media format can be used only with a certificate that can be obtained by the Windows Media SDK from Microsoft.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Software Developer (Senior) G. LABOURE
France France
No Biography provided

Comments and Discussions

Questioncapture MICROPHONE audio and save it in MP3 Pin
aj_scorpio25-Nov-14 20:05
Memberaj_scorpio25-Nov-14 20:05 
QuestionAnd for Windows CE 6.0 ? Pin
gleard28-May-14 0:31
Membergleard28-May-14 0:31 
Questionmpeg1 layer 3 Pin
vaibhavbvp30-Jul-12 0:24
Membervaibhavbvp30-Jul-12 0:24 
AnswerRe: mpeg1 layer 3 Pin
Guitool6-Dec-12 4:00
MemberGuitool6-Dec-12 4:00 
GeneralRe: mpeg1 layer 3 Pin
vaibhavbvp8-Dec-12 20:57
Membervaibhavbvp8-Dec-12 20:57 
Questionacknowledgment Pin
sardasht24-Mar-12 20:39
Membersardasht24-Mar-12 20:39 
Generalquestion Pin
vivek108884-Aug-11 4:49
Membervivek108884-Aug-11 4:49 
QuestionAnybody still here?? Can help? Pin
Jayxian20-Jan-10 16:36
MemberJayxian20-Jan-10 16:36 
GeneralSource Licence Pin
Michael Shazam12-Jun-08 3:52
MemberMichael Shazam12-Jun-08 3:52 
GeneralConvert Pin
Sayyed Mostafa Hashemi23-Apr-08 21:47
MemberSayyed Mostafa Hashemi23-Apr-08 21:47 
GeneralConvert Pin
Sayyed Mostafa Hashemi23-Apr-08 21:47
MemberSayyed Mostafa Hashemi23-Apr-08 21:47 
GeneralMedia player not supported the file Pin
raseena00912-Feb-08 23:05
Memberraseena00912-Feb-08 23:05 
Generalfatal error C1083: Cannot open include file: 'dshow.h': No such file or directory Pin
Le@rner29-Jan-08 19:19
MemberLe@rner29-Jan-08 19:19 
GeneralRe: fatal error C1083: Cannot open include file: 'dshow.h': No such file or directory Pin
YudhaPH9-Feb-08 2:28
professionalYudhaPH9-Feb-08 2:28 
QuestionHow to convert wav to another wav with different sample rates Pin
ruilinxiang25-Dec-07 21:04
Memberruilinxiang25-Dec-07 21:04 
QuestionHow to convert wav to another wav with different sample rates??? Pin
ruilinxiang25-Dec-07 21:04
Memberruilinxiang25-Dec-07 21:04 
Generalbuilding lame dshow Pin
R Thompson8-Nov-07 7:23
MemberR Thompson8-Nov-07 7:23 
GeneralWave Parsing Pin
Sonia Gupta16-May-07 21:40
MemberSonia Gupta16-May-07 21:40 
GeneralA Question about DShowEncoder Pin
chocm7-Mar-07 2:22
Memberchocm7-Mar-07 2:22 
GeneralRe: A Question about DShowEncoder Pin
eurekarex2-Jun-07 20:26
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Generalplz help Pin
sisaym23-Jan-07 19:41
Membersisaym23-Jan-07 19:41 
GeneralRe: plz help Pin
FlyingTinman26-Jan-07 14:28
MemberFlyingTinman26-Jan-07 14:28 
QuestionAnyone tried this under vista? Pin
gourmettt29-Nov-06 1:59
Membergourmettt29-Nov-06 1:59 
AnswerRe: Anyone tried this under vista? Pin
AcAriA9-Apr-07 23:02
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GeneralRe: Anyone tried this under vista? Pin
furbo26-Jun-07 22:34
Memberfurbo26-Jun-07 22:34 

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