doc/encoders: add flac

Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/encoders.texi

@@ -494,6 +494,85 @@ Selected by Encoder (default)
 
 @end table
 
+@anchor{flac}
+@section flac
+
+FLAC (Free Lossless Audio Codec) Encoder
+
+@subsection Options
+
+The following options are supported by FFmpeg's flac encoder.
+
+@table @option
+@item compression_level
+Sets the compression level, which chooses defaults for many other options
+if they are not set explicitly.
+
+@item frame_size
+Sets the size of the frames in samples per channel.
+
+@item lpc_coeff_precision
+Sets the LPC coefficient precision, valid values are from 1 to 15, 15 is the
+default.
+
+@item lpc_type
+Sets the first stage LPC algorithm
+@table @samp
+@item none
+LPC is not used
+
+@item fixed
+fixed LPC coefficients
+
+@item levinson
+
+@item cholesky
+@end table
+
+@item lpc_passes
+Number of passes to use for Cholesky factorization during LPC analysis
+
+@item min_partition_order
+The minimum partition order
+
+@item max_partition_order
+The maximum partition order
+
+@item prediction_order_method
+@table @samp
+@item estimation
+@item 2level
+@item 4level
+@item 8level
+@item search
+Bruteforce search
+@item log
+@end table
+
+@item ch_mode
+Channel mode
+@table @samp
+@item auto
+The mode is chosen automatically for each frame
+@item indep
+Chanels are independently coded
+@item left_side
+@item right_side
+@item mid_side
+@end table
+
+@item exact_rice_parameters
+Chooses if rice parameters are calculated exactly or approximately.
+if set to 1 then they are chosen exactly, which slows the code down slightly and
+improves compression slightly.
+
+@item multi_dim_quant
+Multi Dimensional Quantization. If set to 1 then a 2nd stage LPC algorithm is
+applied after the first stage to finetune the coefficients. This is quite slow
+and slightly improves compression.
+
+@end table
+
 @anchor{libfaac}
 @section libfaac