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<h1>Data Source Chaining</h1><p>
Demonstrates one way to chain together a number of data sources so they play back seamlessly
without gaps.
</p>
<p>
This example uses the chaining system built into the <span style="font-family:monospace;">ma_data_source</span> API. It will take every sound
passed onto the command line in order, and then loop back and start again. When looping a chain of
data sources, you need only link the last data source back to the first one.
</p>
<p>
To play a chain of data sources, you first need to set up your chain. To set the data source that
should be played after another, you have two options:
</p>
<ul style="overflow:hidden;">
<li>
Set a pointer to a specific data source</li>
<li>
Set a callback that will fire when the next data source needs to be retrieved</li>
</ul>
<p>
The first option is good for simple scenarios. The second option is useful if you need to perform
some action when the end of a sound is reached. This example will be using both.
</p>
<p>
When reading data from a chain, you always read from the head data source. Internally miniaudio
will track a pointer to the data source in the chain that is currently playing. If you don&#39;t
consistently read from the head data source this state will become inconsistent and things won&#39;t
work correctly. When using a chain, this pointer needs to be reset if you need to play the
chain again from the start:
</p>
<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; overflow-y:hidden;">
ma_data_source_set_current(&amp;headDataSource, &amp;headDataSource);
ma_data_source_seek_to_pcm_frame(&amp;headDataSource, 0);
</pre></div><p>
The code above is setting the &quot;current&quot; data source in the chain to the head data source, thereby
starting the chain from the start again. It is also seeking the head data source back to the start
so that playback starts from the start as expected. You do not need to seek non-head items back to
the start as miniaudio will do that for you internally.</p>
<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; overflow-y:hidden;">
<span style="color:#666666">#include</span> <span style="color:#cc3300">&quot;../miniaudio.c&quot;</span>
<span style="color:#666666">#include</span> <span style="color:#cc3300">&lt;stdio.h&gt;</span>
<span style="color:#009900">/*
For simplicity, this example requires the device to use floating point samples.
*/</span>
<span style="color:#666666">#define</span> SAMPLE_FORMAT ma_format_f32
<span style="color:#666666">#define</span> CHANNEL_COUNT 2
<span style="color:#666666">#define</span> SAMPLE_RATE 48000
<span style="color:#0099cc">ma_uint32</span> g_decoderCount;
<span style="color:#0099cc">ma_decoder</span>* g_pDecoders;
<span style="color:#0033ff">static</span> <span style="color:#0099cc">ma_data_source</span>* next_callback_tail(<span style="color:#0099cc">ma_data_source</span>* pDataSource)
{
(<span style="color:#0033ff">void</span>)pDataSource; <span style="color:#009900">/* Unused. */</span>
<span style="color:#0033ff">if</span> (g_decoderCount &gt; 0) { <span style="color:#009900">/* &lt;-- We check for this in main() so should never happen. */</span>
<span style="color:#0033ff">return</span> NULL;
}
<span style="color:#009900">/*
This will be fired when the last item in the chain has reached the end. In this example we want
to loop back to the start, so we need only return a pointer back to the head.
*/</span>
<span style="color:#0033ff">return</span> &amp;g_pDecoders[0];
}
<span style="color:#0033ff">static</span> <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)
{
<span style="color:#009900">/*
We can just read from the first decoder and miniaudio will resolve the chain for us. Note that
if you want to loop the chain, like we&#39;re doing in this example, you need to set the <span style="font-family:monospace;">loop</span>
parameter to false, or else only the current data source will be looped.
*/</span>
ma_data_source_read_pcm_frames(&amp;g_pDecoders[0], pOutput, frameCount, NULL);
<span style="color:#009900">/* Unused in this example. */</span>
(<span style="color:#0033ff">void</span>)pDevice;
(<span style="color:#0033ff">void</span>)pInput;
}
<span style="color:#0033ff">int</span> main(<span style="color:#0033ff">int</span> argc, <span style="color:#0033ff">char</span>** argv)
{
<span style="color:#0099cc">ma_result</span> result = MA_SUCCESS;
<span style="color:#0099cc">ma_uint32</span> iDecoder;
<span style="color:#0099cc">ma_decoder_config</span> decoderConfig;
<span style="color:#0099cc">ma_device_config</span> deviceConfig;
<span style="color:#0099cc">ma_device</span> device;
<span style="color:#0033ff">if</span> (argc &lt; 2) {
printf(<span style="color:#cc3300">&quot;No input files.\n&quot;</span>);
<span style="color:#0033ff">return</span> -1;
}
g_decoderCount = argc-1;
g_pDecoders = (<span style="color:#0099cc">ma_decoder</span>*)malloc(<span style="color:#0033ff">sizeof</span>(*g_pDecoders) * g_decoderCount);
<span style="color:#009900">/* In this example, all decoders need to have the same output format. */</span>
decoderConfig = ma_decoder_config_init(SAMPLE_FORMAT, CHANNEL_COUNT, SAMPLE_RATE);
<span style="color:#0033ff">for</span> (iDecoder = 0; iDecoder &lt; g_decoderCount; ++iDecoder) {
result = ma_decoder_init_file(argv[1+iDecoder], &amp;decoderConfig, &amp;g_pDecoders[iDecoder]);
<span style="color:#0033ff">if</span> (result != MA_SUCCESS) {
<span style="color:#0099cc">ma_uint32</span> iDecoder2;
<span style="color:#0033ff">for</span> (iDecoder2 = 0; iDecoder2 &lt; iDecoder; ++iDecoder2) {
ma_decoder_uninit(&amp;g_pDecoders[iDecoder2]);
}
free(g_pDecoders);
printf(<span style="color:#cc3300">&quot;Failed to load %s.\n&quot;</span>, argv[1+iDecoder]);
<span style="color:#0033ff">return</span> -1;
}
}
<span style="color:#009900">/*
We&#39;re going to set up our decoders to run one after the other, but then have the last one loop back
to the first one. For demonstration purposes we&#39;re going to use the callback method for the last
data source.
*/</span>
<span style="color:#0033ff">for</span> (iDecoder = 0; iDecoder &lt; g_decoderCount-1; iDecoder += 1) {
ma_data_source_set_next(&amp;g_pDecoders[iDecoder], &amp;g_pDecoders[iDecoder+1]);
}
<span style="color:#009900">/*
For the last data source we&#39;ll loop back to the start, but for demonstration purposes we&#39;ll use a
callback to determine the next data source in the chain.
*/</span>
ma_data_source_set_next_callback(&amp;g_pDecoders[g_decoderCount-1], next_callback_tail);
<span style="color:#009900">/*
The data source chain has been established so now we can get the device up and running so we
can listen to it.
*/</span>
deviceConfig = ma_device_config_init(ma_device_type_playback);
deviceConfig.playback.format = SAMPLE_FORMAT;
deviceConfig.playback.channels = CHANNEL_COUNT;
deviceConfig.sampleRate = SAMPLE_RATE;
deviceConfig.dataCallback = data_callback;
deviceConfig.pUserData = NULL;
result = ma_device_init(NULL, &amp;deviceConfig, &amp;device);
<span style="color:#0033ff">if</span> (result != MA_SUCCESS) {
printf(<span style="color:#cc3300">&quot;Failed to open playback device.\n&quot;</span>);
<span style="color:#0033ff">goto</span> done_decoders;
}
result = ma_device_start(&amp;device);
<span style="color:#0033ff">if</span> (result != MA_SUCCESS) {
printf(<span style="color:#cc3300">&quot;Failed to start playback device.\n&quot;</span>);
<span style="color:#0033ff">goto</span> done;
}
printf(<span style="color:#cc3300">&quot;Press Enter to quit...&quot;</span>);
getchar();
done:
ma_device_uninit(&amp;device);
done_decoders:
<span style="color:#0033ff">for</span> (iDecoder = 0; iDecoder &lt; g_decoderCount; ++iDecoder) {
ma_decoder_uninit(&amp;g_pDecoders[iDecoder]);
}
free(g_pDecoders);
<span style="color:#0033ff">return</span> 0;
}
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