SAMPLE: Direct-to-Disk Recorder with ACM

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SUMMARY

DDREC is a sample that shows how to use the low-level multimedia application programming interface (API) to perform direct-to-disk recording of sound using real-time audio compression from an application for Windows written in the C language.

Download DDREC.EXE, a self-extracting file, from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download DDREC.EXE (size: 41034 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get DDREC.EXE (size: 41034 bytes) 
  

MORE INFORMATION

The Windows MCI commands may be used to record wave audio data from within an application. However, MCI is implemented as a high-level interface. This implementation does not provide extensive control over the recording process, and does not provide easy access to the recorded data.

For more control over data access and the recording process, the low-level multimedia API may be used. If you know ahead of time how much memory will be required for the entire recording, and you know that the required amount is available, you may use a simple one-shot recording procedure (ie: memory allocate, open device, record, close device). In the wave audio recording world, huge memory requirements are common and this process may not be be applicable.

If, however, you do not know the total recording, and/or you want to keep memory requirements to a minimum, a direct-to-disk process may be desirable. This is also known as a double buffer approach, which repeats the process of writing one filled buffer to a disk file while recording another.

DDREC uses two buffers of approximately 32K each that are locally allocated at program startup. When the record process is initiated, the wave buffers are added to the input queue and recording begins. When the first buffer is filled, it is written to a temporary file while the second buffer is filled. After the buffer is written the buffer is queued to for wave audio input again. This procedure is repeated for each buffer until the user stops the recording.

DDREC shows how to use these same two buffers for playing the audio as well as recording using a similar double buffer approach. It also uses the multimedia input/output (mmio*) procedures for reading and saving the wave data in a .WAV format RIFF file.

DDREC also implements the WAVEFORMATEX structure for handling other wave formats besides PCM. It handles compressed formats auomatically using function calls to the Audio Compresison Manager (ACM).