SAMPLE: Direct-to-Disk Recorder with ACM

ID: Q116293

The information in this article applies to:

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.

MORE INFORMATION

The following file is available for download from the Microsoft Software Library: 

 ~ DDREC.EXE (size: 41034 bytes)
For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base: 

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from
               Online Services
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 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 automatically using function calls to the Audio Compression Manager (ACM).

Additional query words: softlib DDREC.EXE acmFormatChoose waveInOpen waveInPrepareHeader waveInStart waveInAddBuffer waveOutOpen waveOutPrepareHeader waveOutWrite 

Keywords          : kbmm kbsample kb16bitonly kbWinOS310 MMWave 
Version           : 3.10
Platform          : WINDOWS

Last Reviewed: December 12, 1998