Encoding Options
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--lax
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Allow encoder to generate non-Subset files. The resulting FLAC file may not be streamable, so you should only use this option in combination with custom encoding options meant for archival. File decoders will still be able play (and seek in) such files.
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-b #
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Set the blocksize. The default is 1152 for -l 0, otherwise 4608. Subset streams must use one of 192/576/1152/2304/4608. The current encoder uses the same blocksize for the entire stream.
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-m
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Enable mid-side coding (only for stereo streams). Tends to increase compression by a few percent on average. For each block both the stereo pair and mid-side versions of the block will be encoded, and smallest resulting frame will be stored. Currently mid-side encoding is only available when bits-per-sample <= 16.
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-0 .. -9
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Fastest compression .. highest compression. The default is -6.
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-0
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Synonymous with -l 0
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-1
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Synonymous with -l 0 -m
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-2
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Synonymous with -l 0 -m -r # (where # is set based on the blocksize)
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-3
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Reserved
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-4
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Synonymous with -l 8
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-5
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Synonymous with -l 8 -m
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-6
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Synonymous with -l 8 -m -r # (where # is set based on the blocksize)
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-7
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Reserved
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-8
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Synonymous with -l 32 -m -r # (where # is set based on the blocksize)
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-9
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Synonymous with -l 32 -m -e -r 99 -p. This is painfully slow but gives you the maximum compression flac can do for a given blocksize.
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-e
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Exhaustive model search (expensive!). Normally the encoder estimates the best model to use and encodes once based on the estimate. With an exhaustive model search, the encoder will generate subframes for every order and use the smallest. If the max LPC order is high this can significantly increase the encode time but can shave off another 0.5%.
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-l #
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Specifies the maximum LPC order. This number must be <= 32. If 0, the encoder will not attempt generic linear prediction, and use only fixed predictors. Using fixed predictors is faster but usually results in files being 5-10% larger.
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-q #
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Specifies the precision of the quantized LP coefficients, in bits. The default is -q 0, which means let the encoder decide based on the signal. Unless you really know your input file it's best to leave this up to the encoder.
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-p
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Do exhaustive LP coefficient quantization optimization. This option overrides any -q option. It is expensive and typically will only improve the compression a tiny fraction of a percent.
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-r #
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Do Rice parameter optimization. By default the encoder uses a single Rice parameter for the subframe's entire residual. With this option, the residual is partitioned into 2^n pieces, each with its own Rice parameter. Higher values of n yield diminishing returns. The most bang for the buck is usually with -r 2 (more for higher blocksizes). This usually shaves off another 1.5%. The technique tends to peak out about when blocksize/(2^n)=128. Use -r 99 to force the highest degree of optimization.
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-V
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Verify the encoding process. With this option, flac will create a parallel decoder that decodes the output of the encoder and compares the result against the original. It will abort immediately with an error if a mismatch occurs. -V increases the total encoding time but is guaranteed to catch any unforseen bug in the encoding process.
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-m-, -e-, -p-, -V-, --lax- can all be used to turn off a particular option.
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