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David Reid
415 lines
17 KiB
HTML
415 lines
17 KiB
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<a href="../index.html" class="doc-navigation">Documentation Home</a><a href="../manual/index.html" class="doc-navigation">Programming Manual</a><a href="index.html" class="doc-navigation ">Examples</a><a href="custom_backend.html" class="doc-navigation doc-navigation-l1 ">Custom Backend</a><a href="custom_decoder.html" class="doc-navigation doc-navigation-l1 ">Custom Decoder</a><a href="data_source_chaining.html" class="doc-navigation doc-navigation-l1 ">Data Source Chaining</a><a href="fixed_size_callback.html" class="doc-navigation doc-navigation-l1 doc-navigation-active">Fixed Size Callback</a><a href="simple_capture.html" class="doc-navigation doc-navigation-l1 ">Simple Capture</a><a href="simple_duplex.html" class="doc-navigation doc-navigation-l1 ">Simple Duplex</a><a href="simple_enumeration.html" class="doc-navigation doc-navigation-l1 ">Simple Enumeration</a><a href="simple_loopback.html" class="doc-navigation doc-navigation-l1 ">Simple Loopback</a><a href="simple_looping.html" class="doc-navigation doc-navigation-l1 ">Simple Looping</a><a href="simple_mixing.html" class="doc-navigation doc-navigation-l1 ">Simple Mixing</a><a href="simple_playback.html" class="doc-navigation doc-navigation-l1 ">Simple Playback</a><a href="simple_playback_sine.html" class="doc-navigation doc-navigation-l1 ">Simple Playback Sine</a><a href="../api/index.html" class="doc-navigation" style="border-bottom:none;">API Reference</a></div></td><td valign="top" style="padding:1em; border-left:solid 1px #bbb;">
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<h1>Fixed Size Callback</h1><p>
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Shows one way to implement a data callback that is called with a fixed frame count.
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</p>
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<p>
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miniaudio does not have built-in support for firing the data callback with fixed sized buffers. In order to support
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this you need to implement a layer that sits on top of the normal data callback. This example demonstrates one way of
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doing this.
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</p>
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<p>
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This example uses a ring buffer to act as the intermediary buffer between the low-level device callback and the fixed
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sized callback. You do not need to use a ring buffer here, but it's a good opportunity to demonstrate how to use
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miniaudio's ring buffer API. The ring buffer in this example is in global scope for simplicity, but you can pass it
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around as user data for the device (device.pUserData).
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</p>
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<p>
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This example only works for output devices, but can be implemented for input devices by simply swapping the direction
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of data movement.</p>
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<div style="font-family:monospace; border:solid 1px #003800; border-left:solid 0.5em #003800; margin:1em 0em; width:100%;"><pre style="margin:0.5em 1em; padding:0; line-height:125%; overflow-x:auto;">
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<span style="color:#666666">#define</span> MINIAUDIO_IMPLEMENTATION
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<span style="color:#666666">#include</span> <span style="color:#cc3300">"../miniaudio.h"</span>
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<span style="color:#666666">#include</span> <span style="color:#cc3300"><stdio.h></span>
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<span style="color:#666666">#define</span> DEVICE_FORMAT ma_format_f32
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<span style="color:#666666">#define</span> DEVICE_CHANNELS 1
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<span style="color:#666666">#define</span> DEVICE_SAMPLE_RATE 48000
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<span style="color:#666666">#define</span> PCM_FRAME_CHUNK_SIZE 1234 <span style="color:#009900">/* <-- Play around with this to control your fixed sized buffer. */</span>
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<span style="color:#0099cc">ma_waveform</span> g_sineWave;
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<span style="color:#0099cc">ma_pcm_rb</span> g_rb; <span style="color:#009900">/* The ring buffer. */</span>
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<span style="color:#0033ff">void</span> data_callback_fixed(<span style="color:#0099cc">ma_device</span>* pDevice, <span style="color:#0033ff">void</span>* pOutput, <span style="color:#0033ff">const</span> <span style="color:#0033ff">void</span>* pInput, <span style="color:#0099cc">ma_uint32</span> frameCount)
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{
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<span style="color:#009900">/*
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This callback will have a guaranteed and consistent size for frameCount. In this example we just fill the output buffer with a sine wave. This
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is where you would handle the callback just like normal, only now you can assume frameCount is a fixed size.
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*/</span>
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printf(<span style="color:#cc3300">"frameCount=%d\n"</span>, frameCount);
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ma_waveform_read_pcm_frames(&g_sineWave, pOutput, frameCount);
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<span style="color:#009900">/* Unused in this example. */</span>
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(<span style="color:#0033ff">void</span>)pDevice;
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(<span style="color:#0033ff">void</span>)pInput;
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}
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<span style="color:#0033ff">void</span> data_callback(<span style="color:#0099cc">ma_device</span>* pDevice, <span style="color:#0033ff">void</span>* pOutput, <span style="color:#0033ff">const</span> <span style="color:#0033ff">void</span>* pInput, <span style="color:#0099cc">ma_uint32</span> frameCount)
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{
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<span style="color:#009900">/*
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This is the device's main data callback. This will handle all of the fixed sized buffer management for you and will call data_callback_fixed()
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for you. You should do all of your normal callback stuff in data_callback_fixed().
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*/</span>
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<span style="color:#0099cc">ma_uint32</span> pcmFramesAvailableInRB;
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<span style="color:#0099cc">ma_uint32</span> pcmFramesProcessed = 0;
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<span style="color:#0099cc">ma_uint8</span>* pRunningOutput = (<span style="color:#0099cc">ma_uint8</span>*)pOutput;
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MA_ASSERT(pDevice->playback.channels == DEVICE_CHANNELS);
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<span style="color:#009900">/*
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The first thing to do is check if there's enough data available in the ring buffer. If so we can read from it. Otherwise we need to keep filling
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the ring buffer until there's enough, making sure we only fill the ring buffer in chunks of PCM_FRAME_CHUNK_SIZE.
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*/</span>
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<span style="color:#0033ff">while</span> (pcmFramesProcessed < frameCount) { <span style="color:#009900">/* Keep going until we've filled the output buffer. */</span>
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<span style="color:#0099cc">ma_uint32</span> framesRemaining = frameCount - pcmFramesProcessed;
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pcmFramesAvailableInRB = ma_pcm_rb_available_read(&g_rb);
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<span style="color:#0033ff">if</span> (pcmFramesAvailableInRB > 0) {
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<span style="color:#0099cc">ma_uint32</span> framesToRead = (framesRemaining < pcmFramesAvailableInRB) ? framesRemaining : pcmFramesAvailableInRB;
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<span style="color:#0033ff">void</span>* pReadBuffer;
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ma_pcm_rb_acquire_read(&g_rb, &framesToRead, &pReadBuffer);
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{
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memcpy(pRunningOutput, pReadBuffer, framesToRead * ma_get_bytes_per_frame(pDevice->playback.format, pDevice->playback.channels));
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}
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ma_pcm_rb_commit_read(&g_rb, framesToRead, pReadBuffer);
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pRunningOutput += framesToRead * ma_get_bytes_per_frame(pDevice->playback.format, pDevice->playback.channels);
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pcmFramesProcessed += framesToRead;
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} <span style="color:#0033ff">else</span> {
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<span style="color:#009900">/*
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There's nothing in the buffer. Fill it with more data from the callback. We reset the buffer first so that the read and write pointers
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are reset back to the start so we can fill the ring buffer in chunks of PCM_FRAME_CHUNK_SIZE which is what we initialized it with. Note
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that this is not how you would want to do it in a multi-threaded environment. In this case you would want to seek the write pointer
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forward via the producer thread and the read pointer forward via the consumer thread (this thread).
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*/</span>
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<span style="color:#0099cc">ma_uint32</span> framesToWrite = PCM_FRAME_CHUNK_SIZE;
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<span style="color:#0033ff">void</span>* pWriteBuffer;
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ma_pcm_rb_reset(&g_rb);
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ma_pcm_rb_acquire_write(&g_rb, &framesToWrite, &pWriteBuffer);
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{
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MA_ASSERT(framesToWrite == PCM_FRAME_CHUNK_SIZE); <span style="color:#009900">/* <-- This should always work in this example because we just reset the ring buffer. */</span>
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data_callback_fixed(pDevice, pWriteBuffer, NULL, framesToWrite);
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}
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ma_pcm_rb_commit_write(&g_rb, framesToWrite, pWriteBuffer);
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}
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}
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<span style="color:#009900">/* Unused in this example. */</span>
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(<span style="color:#0033ff">void</span>)pInput;
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}
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<span style="color:#0033ff">int</span> main(<span style="color:#0033ff">int</span> argc, <span style="color:#0033ff">char</span>** argv)
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{
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<span style="color:#0099cc">ma_waveform_config</span> waveformConfig;
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<span style="color:#0099cc">ma_device_config</span> deviceConfig;
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<span style="color:#0099cc">ma_device</span> device;
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waveformConfig = ma_waveform_config_init(DEVICE_FORMAT, DEVICE_CHANNELS, DEVICE_SAMPLE_RATE, ma_waveform_type_sine, 0.1, 220);
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ma_waveform_init(&waveformConfig, &g_sineWave);
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ma_pcm_rb_init(DEVICE_FORMAT, DEVICE_CHANNELS, PCM_FRAME_CHUNK_SIZE, NULL, NULL, &g_rb);
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deviceConfig = ma_device_config_init(ma_device_type_playback);
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deviceConfig.playback.format = DEVICE_FORMAT;
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deviceConfig.playback.channels = DEVICE_CHANNELS;
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deviceConfig.sampleRate = DEVICE_SAMPLE_RATE;
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deviceConfig.dataCallback = data_callback;
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deviceConfig.pUserData = NULL; <span style="color:#009900">/* <-- Set this to a pointer to the ring buffer if you don't want it in global scope. */</span>
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<span style="color:#0033ff">if</span> (ma_device_init(NULL, &deviceConfig, &device) != MA_SUCCESS) {
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printf(<span style="color:#cc3300">"Failed to open playback device.\n"</span>);
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ma_pcm_rb_uninit(&g_rb);
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<span style="color:#0033ff">return</span> -4;
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}
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printf(<span style="color:#cc3300">"Device Name: %s\n"</span>, device.playback.name);
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<span style="color:#0033ff">if</span> (ma_device_start(&device) != MA_SUCCESS) {
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printf(<span style="color:#cc3300">"Failed to start playback device.\n"</span>);
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ma_pcm_rb_uninit(&g_rb);
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ma_device_uninit(&device);
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<span style="color:#0033ff">return</span> -5;
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}
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printf(<span style="color:#cc3300">"Press Enter to quit...\n"</span>);
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getchar();
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ma_device_uninit(&device);
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ma_pcm_rb_uninit(&g_rb);
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(<span style="color:#0033ff">void</span>)argc;
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(<span style="color:#0033ff">void</span>)argv;
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<span style="color:#0033ff">return</span> 0;
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}
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</pre></div></td>
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