Direct-to-Disk Recorder with ACM (116293)
The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1
This article was previously published under Q116293 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 INFORMATIONThe following files are available for download from the Microsoft
Download Center: Ddrec.exe
For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:
119591 How to Obtain Microsoft Support Files from Online Services
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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).
Modification Type: | Minor | Last Reviewed: | 8/30/2004 |
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Keywords: | kb16bitonly kbfile kbmm kbsample KB116293 |
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