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:

MPEG1 (32, 44.1, 48 kHz)
MPEG2 (16, 22.05, 24 kHz)
MPEG2.5 (8, 11.025, 12 kHz)

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:

2: near-best quality, not too slow (recommended)
5: good quality, fast
7: ok quality, really fast

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).

val set_private : encoder -> bool -> unit

Get/set private bit.

val get_private : encoder -> bool

val set_copyright : encoder -> bool -> unit

Get/set copyright bit.

val get_copyright : encoder -> bool

val set_original : encoder -> bool -> unit

Get/set original bit.

val get_original : encoder -> bool

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).