# FLAC encoder

Video Capture SDK .Net Video Edit SDK .Net Media Blocks SDK .Net

The FLAC (Free Lossless Audio Codec) encoder provides high-quality lossless audio compression while preserving the original audio quality.

VideoCaptureCoreX VideoEditCoreX MediaBlocksPipeline

The FLAC encoder supports a wide range of audio configurations:

• Sample rates from 1 Hz to 655,350 Hz
• Up to 8 audio channels (mono to 7.1 surround)
• Lossless compression with adjustable quality settings
• Streamable output support
• Configurable block sizes and compression parameters

The encoder provides a quality parameter ranging from 0 to 9:

• 0: Fastest compression (lowest CPU usage)
• 1-7: Balanced compression settings
• 8: Highest compression (higher CPU usage)
• 9: Insane compression (extremely CPU intensive)

The default quality setting is 5, which offers a good balance between compression ratio and processing speed.

The cross-platform FLACEncoderSettings class offers advanced configuration options:

// Create FLAC encoder settings with default quality
var flacSettings = new FLACEncoderSettings
{
    // Default compression level
    Quality = 5,        

    // Audio block size in samples
    BlockSize = 4608,              

    // Enable streaming support
    StreamableSubset = true,    

    // Enable stereo processing
    MidSideStereo = true          
};

// Create FLAC encoder settings with advanced configuration
var advancedSettings = new FLACEncoderSettings
{
    // Linear Prediction settings
    // Maximum LPC order for prediction
    MaxLPCOrder = 8,               
    // Auto precision for coefficients
    QlpCoeffPrecision = 0,        
    
    // Residual coding settings
    MinResidualPartitionOrder = 3,
    MaxResidualPartitionOrder = 3,
    
    // Search optimization settings
    // Disable expensive coefficient search
    ExhaustiveModelSearch = false, 
    // Disable precision search
    QlpCoeffPrecSearch = false,    
    // Disable escape code search
    EscapeCoding = false          
};

Add the FLAC output to the Video Capture SDK core instance:

// Create a Video Capture SDK core instance
var core = new VideoCaptureCoreX();

// Create a FLAC output instance
var flacOutput = new FLACOutput("output.flac");

// Set the quality of the FLAC encoder
flacOutput.Audio.Quality = 5;

// Add the FLAC output
core.Outputs_Add(flacOutput, true);

Set the output format for the Video Edit SDK core instance:

// Create a Video Edit SDK core instance
 var core = new VideoEditCoreX();

// Create a FLAC output instance
 var flacOutput = new FLACOutput("output.flac");

 // Set the quality 
 flacOutput.Audio.Quality = 5;

 // Set the output format
 core.Output_Format = flacOutput;

Create a Media Blocks FLAC output instance:

// Create a FLAC encoder settings instance
var flacSettings = new FLACEncoderSettings();

// Create a FLAC output instance
var flacOutput = new FLACOutputBlock("output.flac", flacSettings);

When configuring the FLAC encoder, consider these performance factors:

1. Higher quality settings (7-9) will significantly increase CPU usage
2. The ExhaustiveModelSearch option can greatly impact encoding speed
3. Larger block sizes may improve compression but increase memory usage
4. StreamableSubset should remain enabled unless you have specific requirements

The encoder supports the following configurations:

• Audio channels: 1 to 8 channels
• Sample rates: 1 Hz to 655,350 Hz
• Bitrate: Variable (lossless compression)

Always check for encoder availability before use:

if (!FLACEncoderSettings.IsAvailable())
{
    // Handle unavailable encoder scenario
    Console.WriteLine("FLAC encoder is not available on this system");
    return;
}

1. Start with the default quality setting (5) and adjust based on your needs
2. Enable MidSideStereo for stereo content to improve compression
3. Use SeekPoints for longer audio files to enable quick seeking
4. Keep StreamableSubset enabled unless you have specific requirements
5. Avoid using ExhaustiveModelSearch unless compression ratio is critical

VideoCaptureCore VideoEditCore

The FLACOutput class provides Windows-only settings for the FLAC encoder. This class implements both IVideoEditBaseOutput and IVideoCaptureBaseOutput interfaces, making it suitable for both video editing and capture scenarios.

• Property: Level
• Type: int
• Range: 0-8
• Default: 5
• Description: Controls the compression level, where 0 provides fastest compression and 8 provides highest compression.

• Property: BlockSize
• Type: int
• Default: 4608
• Valid Values: For subset streams, must be one of:
  • 192, 256, 512, 576, 1024, 1152, 2048, 2304, 4096, 4608
  • 8192, 16384 (only if sample rate > 48kHz)
• Description: Specifies the block size in samples. The encoder uses the same block size for the entire stream.

• Property: LPCOrder
• Type: int
• Default: 8
• Constraints:
  • Must be ≤ 32
  • For subset streams at ≤ 48kHz, must be ≤ 12
• Description: Specifies the maximum Linear Predictive Coding order. Setting to 0 disables generic linear prediction and uses only fixed predictors, which is faster but typically results in 5-10% larger files.

• Property: MidSideCoding
• Type: bool
• Default: false
• Description: Enables mid-side coding for stereo streams. This typically increases compression by a few percent by encoding both stereo pair and mid-side versions of each block and selecting the smallest resulting frame.

• Property: AdaptiveMidSideCoding
• Type: bool
• Default: false
• Description: Enables adaptive mid-side coding for stereo streams. This provides faster encoding than full mid-side coding but with slightly less compression by adaptively switching between independent and mid-side coding.

• Property: RiceMin
• Type: int
• Default: 3
• Description: Sets the minimum residual partition order. Works in conjunction with RiceMax to control how the residual signal is partitioned.

• Property: RiceMax
• Type: int
• Default: 3
• Description: Sets the maximum residual partition order. The residual is partitioned into 2^{min to 2}max pieces, each with its own Rice parameter. Optimal settings typically depend on block size, with best results when blocksize/(2^n)=128.

• Property: ExhaustiveModelSearch
• Type: bool
• Default: false
• Description: Enables exhaustive model search for optimal encoding. When enabled, the encoder generates subframes for every order and uses the smallest, potentially improving compression by ~0.5% at the cost of significantly increased encoding time.

public FLACOutput()

Initializes a new instance with default values:

• Level = 5
• RiceMin = 3
• RiceMax = 3
• LPCOrder = 8
• BlockSize = 4608

public string Save()

Serializes the settings to a JSON string.

public static FLACOutput Load(string json)

Creates a new FLACOutput instance from a JSON string.

var flacSettings = new FLACOutput
{
    Level = 8,                   // Maximum compression
    BlockSize = 4608,            // Default block size
    MidSideCoding = true,        // Enable mid-side coding for better compression
    ExhaustiveModelSearch = true // Enable exhaustive search for best compression
};

core.Output_Format = flacSettings; // Core is VideoCaptureCore or VideoEditCore

1. Compression Level Selection

   • Use Level 0-3 for faster encoding with moderate compression
   • Use Level 4-6 for balanced compression/speed
   • Use Level 7-8 for maximum compression regardless of speed

2. Block Size Considerations

   • Larger block sizes generally provide better compression
   • Stick to standard values (4608, 4096, etc.) for maximum compatibility
   • Consider memory constraints when selecting block size

3. Mid-Side Coding

   • Enable for stereo content when compression is priority
   • Use adaptive mode when encoding speed is important
   • Disable for mono content as it has no effect

4. Rice Parameters

   • Default values (3,3) are suitable for most use cases
   • Increase for potentially better compression at the cost of encoding speed
   • Values beyond 6 rarely provide significant benefits