使用 C libwebsockets 将音频流保存在文件中

Question

我有一个使用 libwebsockets 的 C 服务器，我想将接收到的音频流保存在磁盘上的文件中。

这是我的代码片段：

#define FILENAME        "/home/ubuntu/Desktop/file.wav"
FILE *received_file;

struct lws_context *Audiocontext;
static int callback_audio(
        struct lws *wsi,
        enum lws_callback_reasons reason,
        void *user, void *in, size_t len)
{
    switch (reason) {
        case LWS_CALLBACK_ESTABLISHED: 
        {
            printf("client is connected\n");
            received_file = fopen(FILENAME, "w+");
            if (received_file == NULL)
            {
                printf("Failed to open file\n");
                exit(EXIT_FAILURE);
            }
        }
        break;
        case LWS_CALLBACK_RECEIVE: {
            if(strcmp((char*)in,"EOS")==0)
            {
                printf("End of stream!\n");
                fclose(received_file);
            }
            else
            {
                fwrite(in, 1, len, received_file);
            }
        }
    }
}

我收到消息 "client is connected" 和文件，但内容不对，我无法播放。我认为使用 fwrite().

将流保存到文件的方式存在问题

客户端正在发送编码为 wav、16Khz、单声道的音频块。这是来自客户端的片段（它是一个 javascript 客户端，完整代码在这里：http://kaljurand.github.io/dictate.js/）。

if (recorder) {
    recorder.stop();
    config.onEvent(MSG_STOP, 'Stopped recording');
    // Push the remaining audio to the server
    recorder.export16kMono(function(blob) {
        socketSend(blob);
        socketSend(TAG_END_OF_SENTENCE);
        recorder.clear();
        }, 'export16kMono');
    config.onEndOfSpeech();
} else {
    config.onError(ERR_AUDIO, "Recorder undefined");
}

客户端运行良好，我将其用于完全相同的任务，但使用的是 Java 服务器。如果有人能告诉我如何将这些音频块保存在有效文件中，我将不胜感激。

Answer 1

我认为你没有在你的 wav 文件中写 header。为此，

您可以编写一些函数来执行此操作，请参阅 specification here

或者您可以使用专用库，例如 libsndfile，使用起来并不复杂：

// instead of fopen, write something like
SF_INFO info;
SNDFILE * sf;

info.samplerate = sample_rate;
info.channels = 1;
info.sections = 1;
info.seekable = 0;
info.frames = 0;
info.format = SF_FORMAT_WAV | SF_FORMAT_PCM_16;

sf = sf_open(filename, SFM_WRITE, &info);

// instead of fwrite, something like
sf_write_short(sf, in, len / sizeof(short));

// and instead of fclose
sf_close(sf);

Answer 2

我没有使用libsndfile，但我在客户端做了些改动。这是当前的 hexdump 输出：

00000000  52 49 46 46 20 60 00 00  57 41 56 45 66 6d 74 20  |RIFF `..WAVEfmt |
00000010  10 00 00 00 01 00 02 00  44 ac 00 00 10 b1 02 00  |........D.......|
00000020  04 00 10 00 64 61 74 61  00 60 00 00 00 00 00 00  |....data.`......|
00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00006020  00 00 00 00 00 00 00 00  00 00 00 00 52 49 46 46  |............RIFF|
00006030  20 60 00 00 57 41 56 45  66 6d 74 20 10 00 00 00  | `..WAVEfmt ....|
00006040  01 00 02 00 44 ac 00 00  10 b1 02 00 04 00 10 00  |....D...........|
00006050  64 61 74 61 00 60 00 00  00 00 00 00 00 00 00 00  |data.`..........|
00006060  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
0000c050  00 00 00 00 00 00 00 00  52 49 46 46 20 60 00 00  |........RIFF `..|
0000c060  57 41 56 45 66 6d 74 20  10 00 00 00 01 00 02 00  |WAVEfmt ........|
0000c070  44 ac 00 00 10 b1 02 00  04 00 10 00 64 61 74 61  |D...........data|
0000c080  00 60 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |.`..............|
0000c090  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*

好像是wav编码的，但是我没有内容

使用 C libwebsockets 将音频流保存在文件中

Save audio stream in file using C libwebsockets

c

audio

libwebsockets