minimp3

minimp3

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

Comparison with keyj's minimp3

Comparison by features:

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

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

Usage

First, we need to initialize the decoder structure:

//#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-standard 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:

    /*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.

At end of stream just pass rest of the buffer, sync procedure should work even with just 1 frame in stream (except for free format and garbage at the end can mess things up, so id3v1 and ape tags must be removed first).

For free format there minimum 3 frames needed to do proper sync: 2 frames to detect frame length and 1 next frame to check detect is good.

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:

…

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:

    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:

    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
• https://github.com/DasZiesel/minimp3-delphi - delphi bindings
• https://github.com/mgeier/minimp3_ex-sys - low-level rust bindings to minimp3_ex

Interesting links

• https://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/
• https://id3.org/mp3Frame
• https://www.datavoyage.com/mpgscript/mpeghdr.htm