Process of audio under Windows
Windows
The processing of the audio is roughly divided into two parts, namely, the audio input, output, and
ACM
Compression processing.
In general
Windows
Can be called such as
SndplaySound
Wait
API (MCI)
To play one
WAV
File, but that is obviously not what we need to do. The audio stream must be processed directly. in
Windows
Next, it also provides a series of
API
To
Wavein
with
Waveout
Starting group
API
That is to do this.
Let's talk about it first. Commonly related
API
for
Waveinopen
(Open an audio input device),
Waveinprepareheader
(For a soon
Waveinaddbuffer
Input buffer prepare the head),
Waveinaddbuffer
(Add an input to the data buffer),
WaveInstart
(start recording),
WaveInClose
(Turning off audio input device), etc., and needs
Waveinopen
A callback function or thread specified in it is called to be called after a data buffer is recorded to process these data, and others related operations.
First you have to determine what callback mode you need, that is, after the audio data of a certain time film is completed,
Windows
The processing of these data will be activated through this callback, which is generally used.
FUNCTION
,
Thread
with
Event
These categories, and more convenient and simple
FUNCTION
with
Thread
.
FUNCTION
The way
Windows
Will call your function, and
Thread
Be
Windows
To activate the thread you specify. These are all
Waveinopen
Present specified. Its function prototype is:
MmResult Waveininken (lphwavein phwi, uint udeviceid, lpwaveformatex pwfx, dWord dwcallback, dword dwcallbackinstance, dword fdwopen);
among them:
PHWI
Is the end of the handle storage address,
UdeviceID
Is an audio device to open
Id
No., generally designated
WAVE_MAPPER
.
DWCallback
The address of the designated callback function or thread, etc.
FDWOPEN
Specify the callback mode,
DWCallbackInstance
To call back
User parameters sent by functions or threads. As for that one
PWFX
Then, the key is the key, it specifies what audio format opens the audio input device,
It is a structure
Waveformatex
:
Typedef struct {word wordettag; word nchannels; dword nsampletes; word nblockAlign; Word wbitsPersample; Word Cbsize;} Word CBSIZE;
Machine
Win9x
The audio compression is selected at the time of installation.
WFormattag
Specify some compressed audio formats, such as
G723.1
,
Ture DSP
, Etc. However, it is generally selected.
Waveformat_pcm
Format, an uncompressed audio format, as for compression, can call the following will be mentioned after recording
ACM
Elite.
NChannels is the number of channels,
1
or
2
.
Nsamplespersec
Sampling per second,
8000
,
11025
,
22050
,
44100
For a few standard values, other non-standard values I have not tried it.
Navgbytespersec
For the average number of bytes per second,
PCM
Mode is equal to
NChannels * nsamplesperspec * wbitsPersample / 8
However, for other compressed audio formats, because many compression methods are carried out according to the time tablets, such as
G723.1
It is
30ms
For a compressed unit, so
Navgbytespersec
Just a probably figure, not accurate, the calculation in the program should not be subject to this amount. This is below the compressed audio output and
ACM
It is very important in audio compression.
NblockAlign
Is a relatively special value, indicating the minimum processing unit when the audio processing is
PCM
Non-compressed, it is
WBITSPERSMPLE * NCHANNELS / 8
And for the non-compression format, it is compressed
/
Unzip the minimum unit, such as
G723.1
It is
30ms
Data size (
20bytes
or
24bytes
).
WBITSPERSMPLE
The number of digits per sample value,
8
or
16
.
CBSIZE
It is said that
Waveformatex
How many bytes of bytes after the standard head, for many non-
PCM
Audio format, have some own definition format parameters, these are closely in standard
Waveformatex
Behind, its size is
CBSIZE
Specify. for
PCM
Format, for
0
Or ignore it.
In this way, after these parameters are specified, you should open the audio input device. The thing you have to do is preparing a few buffers that use the recording. Multiple buffers are often prepared and cycled in the callback. In addition, you have to consider the audio data that recorded, such as a temporary file, you have to prepare the handle of the file. For buffer, use
WaveinPerPareHeader
Prepare the head, this
API
It's relatively simple, if you are cycled using buffers, you only need to call each buffer.
Waveinprepareheader
.
After everything is ready, you can call
Waveinaddbuffer
with
WaveInstart
Start recording, as long as you call this
WaveInstart
The recording begins. Even after this buffer is recorded, you didn't join the new buffer in, the recording will not stop, but the speech data in this is lost. Pass
Waveinaddbuffer
After the buffer sent is recorded,
Windows
Will pass you
Waveinopen
The callback is made in the way, and the recorded voice data is taken out in the callback, and if you want to continue recording, you have to add the next buffer into it. Considering this processing is time delay, and the audio is very sensitive to time, usually must first prepare several buffers, for example, a total of a total definition
8
A buffer, and for insurance, it is best to ensure that at least
3
The buffer can be recorded, then add it when starting recording.
4
A buffer, then in the callback, if the current buffer is
n
Others
(N 4)% 8
transfer
Waveinaddbuffer
At this time, there is also the first
(N 1)% 8, (N 2)% 8, (N 3)% 8
These three buffers can be used, ie, can guarantee that there is no disconnected interval in the recorded audio.
Want to end recording, it is best
WaveInClose
Call before
WaveinReset
This can clear the buffer still waiting for the recording, and must pay attention to the type of message in the parameter in the callback.
The audio output is relatively simple. corresponding
API
Have
Waveoutopen
,
WaveoutPrepareHeader
,
Waveoutwrite
as well as
WaveoutClose
. If you want to directly output an audio of the compressed format, you must pay attention
Waveoutopen
The audio format parameters specified in the middle. You must be aware of the specific parameters of this type of format and its meaning. However, you can pass the following
ACM
(
Audio Compress Manager
) Get the specific parameters of the audio format you need, this format parameter can be used directly
Waveoutopen
. Like the input of audio,
WaveoutPrepareHeader
It is also necessary.
Waveoutwrite
It is to fill in the output buffer. In order to avoid interruption, it should also ensure that the number of buffer queues in a certain moment is sufficient.
If installed
Win98
When the audio compression is selected in the attachment, then on the machine
ACM
It can be used.
ACM
for
Audio Compress Manager
.
Win98
Provides some common audio compression algorithm package for user calls. able to pass
ACM
Get all audio compression drives on this unit and its supported audio format. However, it doesn't seem to be every
ACM
Format can be called to compress
,
but
ACM
Most of the compression drives are directed to the voice band. If the audio used to compress the frequency band, such as music, the effect is very poor.
.
