Module Flac.Decoder

Decode native FLAC data

Usage

A typical use of the FLAC decoder is the following: * * 

 (* Raise this when streams has ended. *)
    * exception End_of_stream
    * (* Define a read function *)
    * let input = (..a function of type read..) in
    * (* Define a write function *)
    * let output = (..a function of type write..) in
    * (* Create callbacks *)
    * let callbacks = Flac.Decoder.get_callbacks input write in
    * (* Create an unitialized decoder *)
    * let decoder = Flac.Decoder.create callbacks in
    * (* Initialize decoder *)
    * let decoder,info,comments = Flac.Decoder.init decoder callbacks in
    * (..do something with info and comments..)
    * (* Decode data *)
    * match Flac.Decoder.state decoder c with
    *   | `Search_for_metadata
    *   | `Read_metadata
    *   | `Search_for_frame_sync
    *   | `Read_frame ->
    *         Flac.Decoder.process decoder callbacks
    *   | _ -> raise End_of_stream

* * Some remarks: * - Exceptions raised by callbacks should be treated * as fatal errors. The dehaviour of the flac library * after being interrupted by an exception is unknown. * The only notable exception is Ogg/flac decoding, where * the read callback raises Ogg.Not_enough_data. * - The state of the decoder should be checked prior to calling * process. Termination may not be detected nor raise an * exception so it is the caller's responsibility to check * on this. * - See FLAC documentation for the information on the * callbacks. * - The variant type for decoder and callbacks is used * to make sure that different type of decoders * (generic, file, ogg) are only used with the same * type of callbacks.

Types

type t
type info = {
  1. sample_rate : int;
  2. channels : int;
  3. bits_per_sample : int;
  4. total_samples : int64;
  5. md5sum : string;
}
type comments = string * (string * string) list

(Vorbis) comments of decoded FLAC data.

type state = [
  1. | `Search_for_metadata
  2. | `Read_metadata
  3. | `Search_for_frame_sync
  4. | `Read_frame
  5. | `End_of_stream
  6. | `Ogg_error
  7. | `Seek_error
  8. | `Aborted
  9. | `Memory_allocation_error
  10. | `Uninitialized
]

Possible states of a decoder.

Exceptions

exception Lost_sync

An error in the stream caused the decoder to lose synchronization.

exception Bad_header

The decoder encountered a corrupted frame header.

exception Frame_crc_mismatch

The frame's data did not match the CRC in the footer.

exception Unparseable_stream

The decoder encountered reserved fields in use in the stream.

exception Not_flac

Raised if trying to decode a stream that * is not flac.

Functions

val create : ?seek:(int64 -> unit) -> ?tell:(unit -> int64) -> ?length:(unit -> int64) -> ?eof:(unit -> bool) -> read:(bytes -> int -> int -> int) -> write:(float array array -> unit) -> unit -> t * info * comments option

Create a decoder. The decoder will be used to decode * all metadata. Initial audio data shall be immediatly available * after this call.

val process : t -> unit

Decode one frame of audio data.

val seek : t -> Stdlib.Int64.t -> bool

Flush the input and seek to an absolute sample. * Decoding will resume at the given sample. Note * that because of this, the next write callback may * contain a partial block. The client must support seeking * the input or this function will fail and return false. * Furthermore, if the decoder state is `Seek_error * then the decoder must be flushed or reset * before decoding can continue.

val flush : t -> bool

Flush the stream input. * The decoder's input buffer will be cleared and the state set to * `Search_for_frame_sync. This will also turn * off MD5 checking.

val reset : t -> bool

Reset the decoding process. * The decoder's input buffer will be cleared and the state set to * `Search_for_metadata. MD5 checking will be restored to its original * setting. * * If the decoder is seekable, the decoder will also attempt to seek to * the beginning of the stream. If this rewind fails, this function will * return false. It follows that reset cannot be used when decoding * from stdin. * * If the decoder is not seekable (i.e. no seek callback was provided) * it is the duty of the client to start feeding data from the beginning * of the stream on the next process.

val state : t -> state

Get the state of a decoder.

Convenience

val to_s16le : float array array -> string

Convert an audio array to a S16LE string for * decoding FLAC to WAV and raw PCM

module File : sig ... end

Local file decoding.