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Module Lame


module Lame: sig .. end
Bindings to the lame library to encode mp3 files.


Author(s): Samuel Mimram


General informations


val get_lame_version : unit -> string
Get the lame version number.
val get_lame_short_version : unit -> string
Get the lame version number (shorter than get_lame_version).
val get_lame_very_short_version : unit -> string
Get the lame version number (shorter than get_lame_short_version).
val get_lame_url : unit -> string
Get the url of the lame website.
val get_psy_version : unit -> string
Get the version of the psy model.

Encoders


type encoder
Type for lame encoders.
val create_encoder : unit -> encoder
Create a new lame encoder.

Parameters


val set_in_samplerate : encoder -> int -> unit
Input sample rate in Hz (default: 44100).
val set_num_channels : encoder -> int -> unit
Number of channels in input stream (default: 2).
val set_out_samplerate : encoder -> int -> unit
Output sample rate in Hz (default: 0, which means LAME picks best value based on the amount of compression). MPEG only allows: 
val set_quality : encoder -> int -> unit
Internal algorithm selection. True quality is determined by the bitrate but this variable will effect quality by selecting expensive or cheap algorithms. The quality is an integer between 0 and 9, where 0=best (very slow) and 9=worst. More precisely:

type mode =
| Stereo (*stereo, channels encoded independely*)
| Joint_stereo (*stereo, channels encoded together*)
| Dual_channel (*not supported*)
| Mono (*mono*)
Compression mode.
val set_mode : encoder -> mode -> unit
Set the compression mode.

type vbr_mode =
| Vbr_off (*constant bitrate*)
| Vbr_rh
| Vbr_abr
| Vbr_mtrh
| Vbr_max_indicator
VBR (Variable BitRate) mode.
val set_vbr_mode : encoder -> vbr_mode -> unit
Set the VBR mode.
val set_vbr_quality : encoder -> int -> unit
Set the VBR quality level (0:highest, 9: lowest).
val set_vbr_mean_bitrate : encoder -> int -> unit
Set the VBR mean birate in kbps. Only used by Vbr_abr mode.
val set_vbr_min_bitrate : encoder -> int -> unit
Set the minimal VBR bitrate in kbps.
val set_vbr_max_bitrate : encoder -> int -> unit
Set the maximal VBR bitrate in kbps.
val set_vbr_hard_min : encoder -> bool -> unit
If true, enforce the minimal VBR bitrate. Normally it will be violated for analog silence.
val set_brate : encoder -> int -> unit
Set the bitrate of compressed data. You can either set this or use set_compression_ratio.
val set_compression_ratio : encoder -> float -> unit
Set the compression ratio (default: 11).
exception Init_params_failed
A call to init_params failed for some reason.
val init_params : encoder -> unit
Initialize lame's parameters. Should be called before encoding (and after having set the parameters). Raises Init_params_failed on error.
val init_bitstream : encoder -> unit
Write id3v2 and Xing headers into the front of the bitstream, and set frame counters and bitrate histogram data to 0. Normally, this is called by init_params. You can call this after encode_flush_nogap.

Encoding


exception Init_params_not_called
You should have called init_params.
exception Psychoacoustic_problem
A problem occured with psychoacoustics.
exception Unknown_error of int
This should not have happened. Please report.
val encode_buffer_part : encoder -> string -> int -> int -> string
encode_buffer_part enc buf ofs smpl encodes samples samples (per channel) of buf starting at position ofs.
val encode_buffer : encoder -> string -> int -> string
Same as encode_buffer_part but with ofs = 0.
val encode_buffer_float_part : encoder -> float array -> float array -> int -> int -> string
encode_buffer_float_part enc left right ofs smpl encodes samples samples of left and right channels starting at position ofs. Floats are expected to range over -1;1.
val encode_buffer_float : encoder -> float array -> float array -> int -> string
Same as encode_buffer_float_part but with ofs = 0.
val encode_flush : encoder -> string
Flush the PCM buffers, padding with zeros if needed to make a complete frame. Will also write id3v1 tags (if any) into the bitstream.
val encode_flush_nogap : encoder -> string
Flush the PCM buffers, padding with zeros if needed to make a complete frame. This function will not write id3v1 tags into the bitstream.

Id3 tags


module Id3tag: sig .. end

Informations about encoding



type mpeg_version =
| Mpeg_1 (*MPEG v1*)
| Mpeg_2 (*MPEG v2*)
| Mpeg_2_5 (*MPEG v2.5*)
MPEG version.
val get_version : encoder -> mpeg_version
The MPEG version used by the encoder.
val get_encoder_delay : encoder -> int
Get the encoder delay.
val get_framesize : encoder -> int
Size of an mpeg frame in bytes.
val get_nb_samples_to_encode : encoder -> int
Number of PCM samples buffered, but not yet encoded to mp3 data.
val get_nb_encoded_frames : encoder -> int
Number of frames encoded so far.
val get_nb_frames : encoder -> int
Estimate of the total number of frames to be encoded (only valid if set_nb_samples was called).