OCamlでWAVファイル読み込んでALSAで再生するテスト

ocaml_alsa_test.ml

(*
 * ocaml_alsa_test.ml
 *
 * Created by fukuroda (https://github.com/fukuroder)
 *)

(* sudo apt-get install libalsa-ocaml-dev *)

(* ocamlfind ocamlopt -o ocaml_alsa_test ocaml_alsa_test.ml -package alsa -linkpkg *)

(* 例外 *)
exception InvalidWavFormat of string

(* 文字列読み込み *)
let read_string f n = (
    let buf = Buffer.create n in (
        Buffer.add_channel buf f n;
        Buffer.contents buf
    )
)

(* 4byte読み込み *)
let read_byte4 f = (
    let rec read_byte4_sub n = (
        let v = Int64.of_int (input_byte f) in
        let v = Int64.shift_left v (n*8) in
        (match n with
        | 3 ->  v
        | _ ->  Int64.logor v (read_byte4_sub (n+1))
        )
    ) in read_byte4_sub 0
)

(* 2byte読み込み *)
let read_byte2 f = (
    let a1 = input_byte f and a2 = input_byte f in (
       (a2 lsl 8) lor a1
    )
)

(* frame読み込み *)
let read_frame buf f pos = (
    buf.[4*pos]   <- input_char f;
    buf.[4*pos+1] <- input_char f;
    buf.[4*pos+2] <- input_char f;
    buf.[4*pos+3] <- input_char f
)

(* block読み込み *)
let read_block buf f block_size = (
    let rec read_block_sub pos = (
        match (block_size-pos) with
        | 0 -> ()
        | _ -> read_frame buf f pos;
               read_block_sub (pos+1)
    ) in read_block_sub 0
)

(* WAVヘッダの読み込みとframe数取得 *)
let get_frames wav = (
    (* RIFFヘッダ *)
    let data = read_string wav 4 in (
        Printf.printf "%s\n" data;
        if data <> "RIFF" then raise (InvalidWavFormat "RIFFでない")
    );

    (* ファイルサイズ - 8 *)
    let data = read_byte4 wav in (
        Printf.printf "%Ld\n" data
    );

    (* WAVEヘッダ *)
    let data = read_string wav 4 in (
        Printf.printf "%s\n" data;
        if data <> "WAVE" then raise (InvalidWavFormat "WAVEでない")
    );

    (* fmtチャンク *)
    let data = read_string wav 4 in (
        Printf.printf "%s\n" data;
        if data <> "fmt " then raise (InvalidWavFormat "fmt でない")
    );

    (* fmtチャンクのバイト数 *)
    let data = read_byte4 wav in (
        Printf.printf "%Ld\n" data;
        if data <> 16L then raise (InvalidWavFormat "fmtチャンクのバイト数が16でない")
    );

    (* フォーマットID *)
    let data = read_byte2 wav in (
        Printf.printf "%d\n" data;
        if data <> 1 then raise (InvalidWavFormat "PCMでない")
    );

    (* チャンネル数 *)
    let data = read_byte2 wav in (
        Printf.printf "%d\n" data;
        if data <> 2 then raise (InvalidWavFormat "stereoでない")
    );

    (* サンプリングレート *)
    let data = read_byte4 wav in (
        Printf.printf "%Ld\n" data;
        if data <> 44100L then raise (InvalidWavFormat "サンプリングレートが44100[kHz]でない")
    );

    (* データ速度 *)
    let data = read_byte4 wav in (
        Printf.printf "%Ld\n" data;
        if data <> 176400L then raise (InvalidWavFormat "データ速度が176400[byte/sec]でない")
    );

    (* ブロックサイズ *)
    let data = read_byte2 wav in (
        Printf.printf "%d\n" data;
        if data <> 4 then raise (InvalidWavFormat "ブロックサイズが4でない")
    );

    (* サンプルあたりのビット数 *)
    let data = read_byte2 wav in (
        Printf.printf "%d\n" data;
        if data <> 16 then raise (InvalidWavFormat "サンプルあたりのビット数が16でない")
    );

    (* dataチャンク *)
    let data = read_string wav 4 in (
        Printf.printf "%s\n" data;
        if data <> "data" then raise (InvalidWavFormat "dataでない")
    );

    (* 波形データのバイト数 *)
    let data = read_byte4 wav in (
        Printf.printf "%Ld\n" data;
        flush stdout;

        Int64.div data 4L (* frame数 *)
    )
)

(* デバイスを開く *)
let open_default_pcm = (
    (* オーディオデバイスを開く *)
    let pcm = Alsa.Pcm.open_pcm "hw:0,0" [Alsa.Pcm.Playback] [] in (
        (* 設定 *)
        let params = Alsa.Pcm.get_params pcm in (
            Alsa.Pcm.set_access pcm params Alsa.Pcm.Access_rw_interleaved;
            Alsa.Pcm.set_format pcm params Alsa.Pcm.Format_s16_le;
            ignore (Alsa.Pcm.set_rate_near pcm params 44100 Alsa.Dir_eq);
            Alsa.Pcm.set_channels pcm params 2;
            Alsa.Pcm.set_buffer_size pcm params (1024*4);
            Alsa.Pcm.set_params pcm params;
        );
        pcm
    )
)

(* PCM書き込み *)
let write_pcm pcm wav frames = (
    let buffer = String.create (2*2*1024)
    and blocks = Int64.div frames 1024L
    and last_block_size = Int64.to_int (Int64.rem frames 1024L) in (
        let rec write_pcm_sub blocks = (
            let block_size = match blocks with
                             | 0L -> last_block_size
                             | _  -> 1024 in (
                read_block buffer wav block_size;
                ignore (Alsa.Pcm.writei pcm buffer 0 block_size);
                match blocks with
                 | 0L -> ()
                 | _  -> write_pcm_sub (Int64.sub blocks 1L)
            )
        ) in write_pcm_sub blocks
    )
)

(* entry *)
let () = (
    let wav = open_in_bin "kmb.wav" in (
        (try
            let frames = get_frames wav  (* フレーム数取得 *)
            and pcm = open_default_pcm   (* オーディオデバイスを開く *)
            in (
                write_pcm pcm wav frames; (* 書き込み *)
                Alsa.Pcm.drain pcm;
                Alsa.Pcm.close pcm        (* オーディオデバイスを閉じる *)
            )
        with
            InvalidWavFormat(s) -> Printf.printf "InvalidWavFormat %s\n" s
        );

        (* ファイルを閉じる *)
        close_in wav;
        Printf.printf "OK\n"
    )
)

(* 結果
RIFF
27570180
WAVE
fmt
16
1
2
44100
176400
4
16
data
27570144
OK
*)