[英]WASAPI Loopback: Save wave file
I want to record the system's audio output using WASAPI and then saving it to a .wav file.我想使用 WASAPI 记录系统的音频输出,然后将其保存到 .wav 文件。
So far I've followed these guides on WASAPI:到目前为止,我已经在 WASAPI 上遵循了这些指南:
https://msdn.microsoft.com/en-us/library/windows/desktop/dd316551%28v=vs.85%29.aspx https://msdn.microsoft.com/en-us/library/windows/desktop/dd370800%28v=vs.85%29.aspx https://msdn.microsoft.com/en-us/library/windows/desktop/dd316551%28v=vs.85%29.aspx https://msdn.microsoft.com/en-us/library/windows/desktop /dd370800%28v=vs.85%29.aspx
I get the buffer data using我使用获取缓冲区数据
audioCaptureClient->GetBuffer(&data, &numFramesAvailable, &flags, NULL, NULL);
then, I'm processing this data, by just writing it at the end of the .wav file:然后,我正在处理这些数据,只需将其写入 .wav 文件的末尾:
size_t dataSize = format.nChannels * (format.wBitsPerSample / 8) * numFramesAvailable;
fwrite(data, dataSize, 1, fp);
format
is a WAVEFORMATEX
received from audioClient->GetMixFormat(&format)
: format
是从audioClient->GetMixFormat(&format)
接收到的WAVEFORMATEX
:
cbSize: 22
nAvgBytesPerSec: 352800
nBlockAlign: 8
nChannels: 2
nSamplesPerSec: 44100
wBitsPerSample: 32
wFormatTag: 65534 (WAVE_FORMAT_EXTENSIBLE)
Apparently the subtype of WAVE_FORMAT_EXTENSIBLE
is Float:显然
WAVE_FORMAT_EXTENSIBLE
的子类型是 Float:
WAVEFORMATEXTENSIBLE *waveformatextensible = (WAVEFORMATEXTENSIBLE *)format;
if (IsEqualGUID(KSDATAFORMAT_SUBTYPE_IEEE_FLOAT, waveformatextensible->SubFormat)) { // true
Before writing all the captured data to the file I fill in the headers (following http://www.topherlee.com/software/pcm-tut-wavformat.html ):在将所有捕获的数据写入文件之前,我填写标题(遵循http://www.topherlee.com/software/pcm-tut-wavformat.html ):
UINT32 sizePlaceholder = 0;
UINT32 fmtLength = 16;
// RIFF Header
fputs("RIFF", fp); // offset 0 (0x00)
fwrite(&sizePlaceholder, 4, 1, fp); // offset 4 (0x04)
fputs("WAVE", fp); // offset 8 (0x08)
// fmt-Section
fputs("fmt ", fp); // offset 12 (0x0C)
fwrite(&fmtLength, 4, 1, fp); // offset 16 (0x10)
fwrite(&format.wFormatTag, 2, 1, fp); // offset 20 (0x14)
fwrite(&format.nChannels, 2, 1, fp); // offset 22 (0x16)
fwrite(&format.nSamplesPerSec, 4, 1, fp); // offset 24 (0x18)
fwrite(&format.nAvgBytesPerSec, 4, 1, fp); // offset 28 (0x1C)
fwrite(&format.nBlockAlign, 2, 1, fp); // offset 32 (0x20)
fwrite(&format.wBitsPerSample, 2, 1, fp); // offset 34 (0x22)
// Data-Section
fputs("data", fp); // offset 36 (0x24)
fwrite(&sizePlaceholder, 4, 1, fp); // offset 40 (0x28)
After finishing writing 3 seconds of data I fill in the placeholders for the file size and the data section size using fwrite
.写完 3 秒的数据后,我使用
fwrite
填充文件大小和数据段大小的占位符。
The file is not being readable.该文件不可读。 I suspect it has to do with
WAVE_FORMAT_EXTENSIBLE
, but I couldn't figure it out.我怀疑它与
WAVE_FORMAT_EXTENSIBLE
,但我无法弄清楚。
I tried overwriting several elements of format
like:我尝试覆盖几个
format
元素,例如:
cbSize = 0;
wFormatTag = WAVE_FORMAT_IEEE_FLOAT;
Producing a readable .wav file, but playing as silence with some clicks in it (I tried recording a song).生成一个可读的 .wav 文件,但在其中播放一些点击时静音(我尝试录制一首歌)。
wFormatTag = WAVE_FORMAT_PCM;
is producing all random noise.正在产生所有随机噪声。
So, finally after long hours of experimenting I found the solution.所以,经过长时间的试验,我终于找到了解决方案。
There were multiple problems with the code.代码存在多个问题。
WAVE_FORMAT_EXTENSIBLE
uses a file layout, being a bit different. WAVE_FORMAT_EXTENSIBLE
使用文件布局,有点不同。 See this great link for more details.fopen
, so the audio data got corrupted, because fwrite
detects newlines ( \\n
) in the data and adds a carriage return ( \\r
).fopen
设置二进制模式,所以音频数据被破坏了,因为fwrite
检测到数据中的换行符 ( \\n
) 并添加一个回车符 ( \\r
)。 I had to use fopen("foo.wav", "wb")
instead of fopen("foo.wav", "w")
.fopen("foo.wav", "wb")
而不是fopen("foo.wav", "w")
。 The second problem, was the decisive reason, because I already tried replacing the WAVE_FORMAT_EXTENSIBLE
-tag with the WAVE_FORMAT_IEEE_FLOAT
-tag, which should have worked, because the additional information are not needed for a .wav file to work.第二个问题是决定性的原因,因为我已经尝试用
WAVE_FORMAT_EXTENSIBLE
标签替换WAVE_FORMAT_IEEE_FLOAT
标签,这应该可以工作,因为 .wav 文件不需要附加信息。
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