如何使用PulseAudio異步庫播放原始PCM數據？

Question

在PulseAudio文檔中似乎缺少一個明確的解釋，我找不到任何簡單的示例。

Answer 1

像這樣

/* 
pcm-playback: pcm-playback.c 
    gcc -o pcm-playback pcm-playback.c `pkg-config --cflags --libs libpulse` 
*/ 

#include <stdio.h> 
#include <assert.h> 
#include <pulse/pulseaudio.h> 

#define FORMAT PA_SAMPLE_U8 
#define RATE 44100 

void context_state_cb(pa_context* context, void* mainloop); 
void stream_state_cb(pa_stream *s, void *mainloop); 
void stream_success_cb(pa_stream *stream, int success, void *userdata); 
void stream_write_cb(pa_stream *stream, size_t requested_bytes, void *userdata); 

int main(int argc, char *argv[]) { 
    pa_threaded_mainloop *mainloop; 
    pa_mainloop_api *mainloop_api; 
    pa_context *context; 
    pa_stream *stream; 

    // Get a mainloop and its context 
    mainloop = pa_threaded_mainloop_new(); 
    assert(mainloop); 
    mainloop_api = pa_threaded_mainloop_get_api(mainloop); 
    context = pa_context_new(mainloop_api, "pcm-playback"); 
    assert(context); 

    // Set a callback so we can wait for the context to be ready 
    pa_context_set_state_callback(context, &context_state_cb, mainloop); 

    // Lock the mainloop so that it does not run and crash before the context is ready 
    pa_threaded_mainloop_lock(mainloop); 

    // Start the mainloop 
    assert(pa_threaded_mainloop_start(mainloop) == 0); 
    assert(pa_context_connect(context, NULL, PA_CONTEXT_NOAUTOSPAWN, NULL) == 0); 

    // Wait for the context to be ready 
    for(;;) { 
     pa_context_state_t context_state = pa_context_get_state(context); 
     assert(PA_CONTEXT_IS_GOOD(context_state)); 
     if (context_state == PA_CONTEXT_READY) break; 
     pa_threaded_mainloop_wait(mainloop); 
    } 

    // Create a playback stream 
    pa_sample_spec sample_specifications; 
    sample_specifications.format = FORMAT; 
    sample_specifications.rate = RATE; 
    sample_specifications.channels = 2; 

    pa_channel_map map; 
    pa_channel_map_init_stereo(&map); 

    stream = pa_stream_new(context, "Playback", &sample_specifications, &map); 
    pa_stream_set_state_callback(stream, stream_state_cb, mainloop); 
    pa_stream_set_write_callback(stream, stream_write_cb, mainloop); 

    // recommended settings, i.e. server uses sensible values 
    pa_buffer_attr buffer_attr; 
    buffer_attr.maxlength = (uint32_t) -1; 
    buffer_attr.tlength = (uint32_t) -1; 
    buffer_attr.prebuf = (uint32_t) -1; 
    buffer_attr.minreq = (uint32_t) -1; 

    // Settings copied as per the chromium browser source 
    pa_stream_flags_t stream_flags; 
    stream_flags = PA_STREAM_START_CORKED | PA_STREAM_INTERPOLATE_TIMING | 
     PA_STREAM_NOT_MONOTONIC | PA_STREAM_AUTO_TIMING_UPDATE | 
     PA_STREAM_ADJUST_LATENCY; 

    // Connect stream to the default audio output sink 
    assert(pa_stream_connect_playback(stream, NULL, &buffer_attr, stream_flags, NULL, NULL) == 0); 

    // Wait for the stream to be ready 
    for(;;) { 
     pa_stream_state_t stream_state = pa_stream_get_state(stream); 
     assert(PA_STREAM_IS_GOOD(stream_state)); 
     if (stream_state == PA_STREAM_READY) break; 
     pa_threaded_mainloop_wait(mainloop); 
    } 

    pa_threaded_mainloop_unlock(mainloop); 

    // Uncork the stream so it will start playing 
    pa_stream_cork(stream, 0, stream_success_cb, mainloop); 

    // Play until we get a character 
    getc(stdin); 
} 

void context_state_cb(pa_context* context, void* mainloop) { 
    pa_threaded_mainloop_signal(mainloop, 0); 
} 

void stream_state_cb(pa_stream *s, void *mainloop) { 
    pa_threaded_mainloop_signal(mainloop, 0); 
} 

void stream_write_cb(pa_stream *stream, size_t requested_bytes, void *userdata) { 
    int bytes_remaining = requested_bytes; 
    while (bytes_remaining > 0) { 
     uint8_t *buffer = NULL; 
     size_t bytes_to_fill = 44100; 
     size_t i; 

     if (bytes_to_fill > bytes_remaining) bytes_to_fill = bytes_remaining; 

     pa_stream_begin_write(stream, (void**) &buffer, &bytes_to_fill); 

     for (i = 0; i < bytes_to_fill; i += 2) { 
      buffer[i] = (i%100) * 40/100 + 44; 
      buffer[i+1] = (i%100) * 40/100 + 44; 
     } 

     pa_stream_write(stream, buffer, bytes_to_fill, NULL, 0LL, PA_SEEK_RELATIVE); 

     bytes_remaining -= bytes_to_fill; 
    } 
} 

void stream_success_cb(pa_stream *stream, int success, void *userdata) { 
    return; 
}