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# Audio Processing
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Audio resampling, channel layout conversion, and sample format transformations using FFmpeg's libswresample for comprehensive audio processing.
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## Capabilities
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### Resampling Context Management
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#### Context Operations
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```java { .api }
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/**
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 * Allocate SwrContext
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 * @return Allocated context or null on failure
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 */
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SwrContext swr_alloc();
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/**
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 * Initialize context after setting parameters
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 * @param s Resampling context
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 * @return >= 0 on success
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 */
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int swr_init(SwrContext s);
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/**
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 * Free resampling context
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 * @param s Pointer to context to free
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 */
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void swr_free(SwrContext s);
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/**
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 * Convert audio samples
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 * @param s Resampling context
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 * @param out Output buffer pointers
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 * @param out_count Maximum output samples per channel
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 * @param in Input buffer pointers
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 * @param in_count Input samples per channel
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 * @return Number of output samples per channel, negative on error
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 */
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int swr_convert(SwrContext s, PointerPointer out, int out_count,
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    PointerPointer in, int in_count);
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```
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**Usage Example:**
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```java
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import org.bytedeco.ffmpeg.swresample.*;
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import static org.bytedeco.ffmpeg.global.swresample.*;
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import static org.bytedeco.ffmpeg.global.avutil.*;
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// Create resampling context
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SwrContext swrContext = swr_alloc();
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// Set input parameters
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av_opt_set_int(swrContext, "in_channel_layout", AV_CH_LAYOUT_STEREO, 0);
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av_opt_set_int(swrContext, "in_sample_rate", 44100, 0);
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av_opt_set_sample_fmt(swrContext, "in_sample_fmt", AV_SAMPLE_FMT_S16, 0);
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// Set output parameters  
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av_opt_set_int(swrContext, "out_channel_layout", AV_CH_LAYOUT_MONO, 0);
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av_opt_set_int(swrContext, "out_sample_rate", 22050, 0);
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av_opt_set_sample_fmt(swrContext, "out_sample_fmt", AV_SAMPLE_FMT_FLTP, 0);
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// Initialize
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int result = swr_init(swrContext);
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if (result < 0) {
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    throw new RuntimeException("Cannot initialize resampler");
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}
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// Convert audio
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PointerPointer inputData = /* ... input audio data ... */;
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PointerPointer outputData = /* ... output buffer ... */;
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int outputSamples = swr_convert(swrContext, outputData, 1024, inputData, 2048);
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System.out.println("Converted " + outputSamples + " samples");
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// Cleanup
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swr_free(swrContext);
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```
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### Channel Layout Operations
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#### Channel Management
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```java { .api }
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/**
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 * Get default channel layout for given number of channels
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 * @param nb_channels Number of channels
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 * @return Channel layout
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 */
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long av_get_default_channel_layout(int nb_channels);
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/**
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 * Get number of channels in layout
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 * @param channel_layout Channel layout
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 * @return Number of channels
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 */
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int av_get_channel_layout_nb_channels(long channel_layout);
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/**
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 * Get channel layout string
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 * @param buf Buffer for result
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 * @param buf_size Buffer size
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 * @param nb_channels Number of channels
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 * @param channel_layout Channel layout
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 * @return 0 on success
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 */
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int av_get_channel_layout_string(BytePointer buf, int buf_size, int nb_channels, long channel_layout);
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```
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## Constants
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### Channel Layouts
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```java { .api }
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// Standard channel layouts
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long AV_CH_LAYOUT_MONO = 0x4;           // Center
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long AV_CH_LAYOUT_STEREO = 0x3;         // Left + Right
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long AV_CH_LAYOUT_2POINT1 = 0x103;      // Stereo + LFE
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long AV_CH_LAYOUT_SURROUND = 0x7;       // Stereo + Center
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long AV_CH_LAYOUT_4POINT0 = 0x107;      // Surround + Back Center
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long AV_CH_LAYOUT_5POINT0 = 0x607;      // 4.0 + Side Left/Right
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long AV_CH_LAYOUT_5POINT1 = 0x70F;      // 5.0 + LFE
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long AV_CH_LAYOUT_7POINT1 = 0x1C07;     // 5.1 + Back Left/Right
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```
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### Sample Formats
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```java { .api }
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// Audio sample formats
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int AV_SAMPLE_FMT_U8 = 0;          // Unsigned 8-bit
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int AV_SAMPLE_FMT_S16 = 1;         // Signed 16-bit
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int AV_SAMPLE_FMT_S32 = 2;         // Signed 32-bit
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int AV_SAMPLE_FMT_FLT = 3;         // Float
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int AV_SAMPLE_FMT_DBL = 4;         // Double
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int AV_SAMPLE_FMT_U8P = 5;         // Unsigned 8-bit planar
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int AV_SAMPLE_FMT_S16P = 6;        // Signed 16-bit planar
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int AV_SAMPLE_FMT_S32P = 7;        // Signed 32-bit planar
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int AV_SAMPLE_FMT_FLTP = 8;        // Float planar
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int AV_SAMPLE_FMT_DBLP = 9;        // Double planar
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```