kolibrios-gitea/contrib/media/minimp3/README.md

minimp3
==========

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Minimalistic, single-header library for decoding MP3. minimp3 is designed to be
small, fast (with SSE and NEON support), and accurate (ISO conformant). You can
find a rough benchmark below, measured using ``perf`` on an i7-6700K, IO
included, no CPU heat to address speedstep:

| Vector      | Hz    | Samples| Sec    | Clockticks | Clockticks per second | PSNR | Max diff |
| ----------- | ----- | ------ | ------ | --------- | ------ | ------ | - |
|compl.bit    | 48000 | 248832 | 5.184  | 14306684  | 2.759M | 124.22 | 1 |
|he_32khz.bit | 32000 | 172800 | 5.4    | 8426158   | 1.560M | 139.67 | 1 |
|he_44khz.bit | 44100 | 472320 | 10.710 | 21296300  | 1.988M | 144.04 | 1 |
|he_48khz.bit | 48000 | 172800 | 3.6    | 8453846   | 2.348M | 139.67 | 1 |
|hecommon.bit | 44100 | 69120  | 1.567  | 3169715   | 2.022M | 133.93 | 1 |
|he_free.bit  | 44100 | 156672 | 3.552  | 5798418   | 1.632M | 137.48 | 1 |
|he_mode.bit  | 44100 | 262656 | 5.955  | 9882314   | 1.659M | 118.00 | 1 |
|si.bit       | 44100 | 135936 | 3.082  | 7170520   | 2.326M | 120.30 | 1 |
|si_block.bit | 44100 | 73728  | 1.671  | 4233136   | 2.533M | 125.18 | 1 |
|si_huff.bit  | 44100 | 86400  | 1.959  | 4785322   | 2.442M | 107.98 | 1 |
|sin1k0db.bit | 44100 | 725760 | 16.457 | 24842977  | 1.509M | 111.03 | 1 |

Conformance test passed on all vectors (PSNR > 96db).

## Comparison with keyj's [minimp3](http://keyj.emphy.de/minimp3/)

Comparison by features:

| Keyj minimp3 | Current |
| ------------ | ------- |
| Fixed point  | Floating point |
| source: 84kb | 70kb |
| binary: 34kb (20kb compressed) | 30kb (20kb) |
| no vector opts | SSE/NEON intrinsics |
| no free format | free format support |

Below, you can find the benchmark and conformance test for keyj's minimp3:


| Vector      | Hz    | Samples| Sec    | Clockticks | Clockticks per second | PSNR | Max diff |
| ----------- | ----- | ------ | ------ | --------- | ------  | ----- | - |
|compl.bit    | 48000 | 248832 | 5.184  | 31849373  | 6.143M  | 71.50 | 41 |
|he_32khz.bit | 32000 | 172800 | 5.4    | 26302319  | 4.870M  | 71.63 | 24 |
|he_44khz.bit | 44100 | 472320 | 10.710 | 41628861  | 3.886M  | 71.63 | 24 |
|he_48khz.bit | 48000 | 172800 | 3.6    | 25899527  | 7.194M  | 71.63 | 24 |
|hecommon.bit | 44100 | 69120  | 1.567  | 20437779  | 13.039M | 71.58 | 25 |
|he_free.bit  | 44100 | 0 | 0  | -  | - | -  | - |
|he_mode.bit  | 44100 | 262656 | 5.955  | 30988984  | 5.203M  | 71.78 | 27 |
|si.bit       | 44100 | 135936 | 3.082  | 24096223  | 7.817M  | 72.35 | 36 |
|si_block.bit | 44100 | 73728  | 1.671  | 20722017  | 12.394M | 71.84 | 26 |
|si_huff.bit  | 44100 | 86400  | 1.959  | 21121376  | 10.780M | 27.80 | 65535 |
|sin1k0db.bit | 44100 | 730368 | 16.561 | 55569636  | 3.355M  | 0.15  | 58814 |

Keyj minimp3 conformance test fails on all vectors (PSNR < 96db), and free
format is unsupported. This caused some problems when it was used
[here](https://github.com/lieff/lvg), and was the main motivation for this work.

## Usage

First, we need to initialize the decoder structure:

```c
//#define MINIMP3_ONLY_MP3
//#define MINIMP3_ONLY_SIMD
//#define MINIMP3_NO_SIMD
//#define MINIMP3_NONSTANDARD_BUT_LOGICAL
//#define MINIMP3_FLOAT_OUTPUT
#define MINIMP3_IMPLEMENTATION
#include "minimp3.h"
...
    static mp3dec_t mp3d;
    mp3dec_init(&mp3d);
```

Note that you must define ``MINIMP3_IMPLEMENTATION`` in exactly one source file.
You can ``#include`` ``minimp3.h`` in as many files as you like.
Also you can use ``MINIMP3_ONLY_MP3`` define to strip MP1/MP2 decoding code.
MINIMP3_ONLY_SIMD define controls generic (non SSE/NEON) code generation (always enabled on x64/arm64 targets).
In case you do not want any platform-specific SIMD optimizations, you can define ``MINIMP3_NO_SIMD``.
MINIMP3_NONSTANDARD_BUT_LOGICAL define saves some code bytes, and enforces non-stadnard but logical behaviour of mono-stereo transition (rare case).
MINIMP3_FLOAT_OUTPUT makes ``mp3dec_decode_frame()`` output to be float instead of short and additional function mp3dec_f32_to_s16 will be available for float->short conversion if needed.

Then. we decode the input stream frame-by-frame:

```c
    /*typedef struct
    {
        int frame_bytes;
        int channels;
        int hz;
        int layer;
        int bitrate_kbps;
    } mp3dec_frame_info_t;*/
    mp3dec_frame_info_t info;
    short pcm[MINIMP3_MAX_SAMPLES_PER_FRAME];
    /*unsigned char *input_buf; - input byte stream*/
    samples = mp3dec_decode_frame(&mp3d, input_buf, buf_size, pcm, &info);
```

The ``mp3dec_decode_frame()`` function decodes one full MP3 frame from the
input buffer, which must be large enough to hold one full frame.

The decoder will analyze the input buffer to properly sync with the MP3 stream,
and will skip ID3 data, as well as any data which is not valid. Short buffers
may cause false sync and can produce 'squealing' artefacts. The bigger the size
of the input buffer, the more reliable the sync procedure. We recommend having
as many as 10 consecutive MP3 frames (~16KB) in the input buffer at a time.

The size of the consumed MP3 data is returned in the ``mp3dec_frame_info_t``
field of the ``frame_bytes`` struct; you must remove the data corresponding to
the ``frame_bytes`` field  from the input buffer before the next decoder
invocation.

The decoding function returns the number of decoded samples. The following cases
are possible:

- **0:** No MP3 data was found in the input buffer
- **384:**  Layer 1
- **576:**  MPEG 2 Layer 3
- **1152:** Otherwise

The following is a description of the possible combinations of the number of
samples and ``frame_bytes`` field values:

- More than 0 samples and ``frame_bytes > 0``:  Succesful decode
- 0 samples and ``frame_bytes >  0``: The decoder skipped ID3 or invalid data
- 0 samples and ``frame_bytes == 0``: Insufficient data

If ``frame_bytes == 0``, the other fields may be uninitialized or unchanged; if
``frame_bytes != 0``, the other fields are available. The application may call
``mp3dec_init()`` when changing decode position, but this is not necessary.

As a special case, the decoder supports already split MP3 streams (for example,
after doing an MP4 demux). In this case, the input buffer must contain _exactly
one_ non-free-format frame.

## Seeking

You can seek to any byte in the stream and call ``mp3dec_decode_frame``; this
will work in almost all cases, but is not completely guaranteed. Probablility of
sync procedure failure lowers when MAX_FRAME_SYNC_MATCHES value grows. Default
MAX_FRAME_SYNC_MATCHES=10 and probablility of sync failure should be very low.
If granule data is accidentally detected as a valid MP3 header, short audio artefacting is
possible.

High-level mp3dec_ex_seek function supports precise seek to sample (MP3D_SEEK_TO_SAMPLE)
using index and binary search.

## Track length detect

If the file is known to be cbr, then all frames have equal size and
lack ID3 tags, which allows us to decode the first frame and calculate all frame
positions as ``frame_bytes * N``. However, because of padding, frames can differ
in size even in this case.

In general case whole stream scan is needed to calculate it's length. Scan can be
omitted if vbr tag is present (added by encoders like lame and ffmpeg), which contains
length info. High-level functions automatically use the vbr tag if present.

## High-level API

If you need only decode file/buffer or use precise seek, you can use optional high-level API.
Just ``#include`` ``minimp3_ex.h`` instead and use following additional functions:

```c
#define MP3D_SEEK_TO_BYTE   0
#define MP3D_SEEK_TO_SAMPLE 1

#define MINIMP3_PREDECODE_FRAMES 2 /* frames to pre-decode and skip after seek (to fill internal structures) */
/*#define MINIMP3_SEEK_IDX_LINEAR_SEARCH*/ /* define to use linear index search instead of binary search on seek */
#define MINIMP3_IO_SIZE (128*1024) /* io buffer size for streaming functions, must be greater than MINIMP3_BUF_SIZE */
#define MINIMP3_BUF_SIZE (16*1024) /* buffer which can hold minimum 10 consecutive mp3 frames (~16KB) worst case */
#define MINIMP3_ENABLE_RING 0      /* enable hardware magic ring buffer if available, to make less input buffer memmove(s) in callback IO mode */

#define MP3D_E_MEMORY  -1
#define MP3D_E_IOERROR -2

typedef struct
{
    mp3d_sample_t *buffer;
    size_t samples; /* channels included, byte size = samples*sizeof(mp3d_sample_t) */
    int channels, hz, layer, avg_bitrate_kbps;
} mp3dec_file_info_t;

typedef size_t (*MP3D_READ_CB)(void *buf, size_t size, void *user_data);
typedef int (*MP3D_SEEK_CB)(uint64_t position, void *user_data);

typedef struct
{
    MP3D_READ_CB read;
    void *read_data;
    MP3D_SEEK_CB seek;
    void *seek_data;
} mp3dec_io_t;

typedef struct
{
    uint64_t samples;
    mp3dec_frame_info_t info;
    int last_error;
    ...
} mp3dec_ex_t;

typedef int (*MP3D_ITERATE_CB)(void *user_data, const uint8_t *frame, int frame_size, int free_format_bytes, size_t buf_size, uint64_t offset, mp3dec_frame_info_t *info);
typedef int (*MP3D_PROGRESS_CB)(void *user_data, size_t file_size, uint64_t offset, mp3dec_frame_info_t *info);

/* decode whole buffer block */
int mp3dec_load_buf(mp3dec_t *dec, const uint8_t *buf, size_t buf_size, mp3dec_file_info_t *info, MP3D_PROGRESS_CB progress_cb, void *user_data);
int mp3dec_load_cb(mp3dec_t *dec, mp3dec_io_t *io, uint8_t *buf, size_t buf_size, mp3dec_file_info_t *info, MP3D_PROGRESS_CB progress_cb, void *user_data);
/* iterate through frames */
int mp3dec_iterate_buf(const uint8_t *buf, size_t buf_size, MP3D_ITERATE_CB callback, void *user_data);
int mp3dec_iterate_cb(mp3dec_io_t *io, uint8_t *buf, size_t buf_size, MP3D_ITERATE_CB callback, void *user_data);
/* streaming decoder with seeking capability */
int mp3dec_ex_open_buf(mp3dec_ex_t *dec, const uint8_t *buf, size_t buf_size, int seek_method);
int mp3dec_ex_open_cb(mp3dec_ex_t *dec, mp3dec_io_t *io, int seek_method);
void mp3dec_ex_close(mp3dec_ex_t *dec);
int mp3dec_ex_seek(mp3dec_ex_t *dec, uint64_t position);
size_t mp3dec_ex_read(mp3dec_ex_t *dec, mp3d_sample_t *buf, size_t samples);
#ifndef MINIMP3_NO_STDIO
/* stdio versions of file load, iterate and stream */
int mp3dec_load(mp3dec_t *dec, const char *file_name, mp3dec_file_info_t *info, MP3D_PROGRESS_CB progress_cb, void *user_data);
int mp3dec_iterate(const char *file_name, MP3D_ITERATE_CB callback, void *user_data);
int mp3dec_ex_open(mp3dec_ex_t *dec, const char *file_name, int seek_method);
#ifdef _WIN32
int mp3dec_load_w(mp3dec_t *dec, const wchar_t *file_name, mp3dec_file_info_t *info, MP3D_PROGRESS_CB progress_cb, void *user_data);
int mp3dec_iterate_w(const wchar_t *file_name, MP3D_ITERATE_CB callback, void *user_data);
int mp3dec_ex_open_w(mp3dec_ex_t *dec, const wchar_t *file_name, int seek_method);
#endif
#endif
```

Use MINIMP3_NO_STDIO define to exclude STDIO functions.
MINIMP3_ALLOW_MONO_STEREO_TRANSITION allows mixing mono and stereo in same file.
In that case ``mp3dec_frame_info_t->channels = 0`` is reported on such files and correct channels number passed to progress_cb callback for each frame in mp3dec_frame_info_t structure.
MP3D_PROGRESS_CB is optional and can be NULL, example of file decoding:

```c
    mp3dec_t mp3d;
    mp3dec_file_info_t info;
    if (mp3dec_load(&mp3d, input_file_name, &info, NULL, NULL))
    {
        /* error */
    }
    /* mp3dec_file_info_t contains decoded samples and info,
       use free(info.buffer) to deallocate samples */
```

Example of file decoding with seek capability:

```c
    mp3dec_ex_t dec;
    if (mp3dec_ex_open(&dec, input_file_name, MP3D_SEEK_TO_SAMPLE))
    {
        /* error */
    }
    /* dec.samples, dec.info.hz, dec.info.layer, dec.info.channels should be filled */
    if (mp3dec_ex_seek(&dec, position))
    {
        /* error */
    }
    mp3d_sample_t *buffer = malloc(dec.samples*sizeof(mp3d_sample_t));
    size_t readed = mp3dec_ex_read(&dec, buffer, dec.samples);
    if (readed != dec.samples) /* normal eof or error condition */
    {
        if (dec.last_error)
        {
            /* error */
        }
    }
```

## Bindings

 * https://github.com/tosone/minimp3 - go bindings
 * https://github.com/notviri/rmp3 - rust `no_std` bindings which don't allocate.
 * https://github.com/germangb/minimp3-rs - rust bindings
 * https://github.com/johangu/node-minimp3 - NodeJS bindings
 * https://github.com/pyminimp3/pyminimp3 - python bindings
 * https://github.com/bashi/minimp3-wasm - wasm bindings

## Interesting links

 * http://keyj.emphy.de/minimp3/
 * https://github.com/technosaurus/PDMP3
 * https://github.com/technosaurus/PDMP2
 * https://github.com/packjpg/packMP3
 * https://sites.google.com/a/kmlager.com/www/projects
 * https://sourceforge.net/projects/mp3dec/
 * http://blog.bjrn.se/2008/10/lets-build-mp3-decoder.html
 * http://www.mp3-converter.com/mp3codec/
 * http://www.multiweb.cz/twoinches/mp3inside.htm
 * https://www.mp3-tech.org/
 * http://id3.org/mp3Frame
 * https://www.datavoyage.com/mpgscript/mpeghdr.htm