mp3dec.c

Go to the documentation of this file.

/*
 * MP3 demuxer
 * Copyright (c) 2003 Fabrice Bellard
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
 
#include <string.h>
 
#include "libavutil/opt.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/dict.h"
#include "libavutil/mathematics.h"
#include "avformat.h"
#include "internal.h"
#include "avio_internal.h"
#include "demux.h"
#include "id3v2.h"
#include "id3v1.h"
#include "replaygain.h"
 
#include "libavcodec/codec_id.h"
#include "libavcodec/mpegaudio.h"
#include "libavcodec/mpegaudiodecheader.h"
 
#define XING_FLAG_FRAMES 0x01
#define XING_FLAG_SIZE   0x02
#define XING_FLAG_TOC    0x04
#define XING_FLAC_QSCALE 0x08
 
#define XING_TOC_COUNT 100
 
 
typedef struct {
    AVClass *class;
    int64_t filesize;
    int xing_toc;
    int start_pad;
    int end_pad;
    int usetoc;
    unsigned frames; /* Total number of frames in file */
    unsigned header_filesize;   /* Total number of bytes in the stream */
    unsigned frame_duration;   /* Frame duration in st->time_base */
    int is_cbr;
} MP3DecContext;
 
enum CheckRet {
    CHECK_WRONG_HEADER = -1,
    CHECK_SEEK_FAILED  = -2,
};
 
static int check(AVIOContext *pb, int64_t pos, uint32_t *header);
 
/* mp3 read */
 
static int mp3_read_probe(const AVProbeData *p)
{
    int max_frames, first_frames = 0;
    int whole_used = 0;
    int frames, ret;
    int framesizes, max_framesizes;
    uint32_t header;
    const uint8_t *buf, *buf0, *buf2, *buf3, *end;
 
    buf0 = p->buf;
    end = p->buf + p->buf_size - sizeof(uint32_t);
    while (buf0 < end && !*buf0)
        buf0++;
 
    max_frames = 0;
    max_framesizes = 0;
    buf = buf0;
 
    for (; buf < end; buf = buf2+1) {
        buf2 = buf;
        for (framesizes = frames = 0; buf2 < end; frames++) {
            MPADecodeHeader h;
            int header_emu = 0;
            int available;
 
            header = AV_RB32(buf2);
            ret = avpriv_mpegaudio_decode_header(&h, header);
            if (ret != 0)
                break;
 
            available = FFMIN(h.frame_size, end - buf2);
            for (buf3 = buf2 + 4; buf3 < buf2 + available; buf3++) {
                uint32_t next_sync = AV_RB32(buf3);
                header_emu += (next_sync & MP3_MASK) == (header & MP3_MASK);
            }
            if (header_emu > 2)
                break;
            framesizes += h.frame_size;
            if (available < h.frame_size) {
                frames++;
                break;
            }
            buf2 += h.frame_size;
        }
        max_frames = FFMAX(max_frames, frames);
        max_framesizes = FFMAX(max_framesizes, framesizes);
        if (buf == buf0) {
            first_frames= frames;
            if (buf2 == end + sizeof(uint32_t))
                whole_used = 1;
        }
    }
    // keep this in sync with ac3 probe, both need to avoid
    // issues with MPEG-files!
    if   (first_frames>=7) return AVPROBE_SCORE_EXTENSION + 2;
    else if (max_frames>200 && p->buf_size < 2*max_framesizes)return AVPROBE_SCORE_EXTENSION;
    else if (max_frames>=4 && p->buf_size < 2*max_framesizes) return AVPROBE_SCORE_EXTENSION / 2;
    else if (ff_id3v2_match(buf0, ID3v2_DEFAULT_MAGIC) && 2*ff_id3v2_tag_len(buf0) >= p->buf_size)
                           return p->buf_size < PROBE_BUF_MAX ? AVPROBE_SCORE_EXTENSION / 4 : AVPROBE_SCORE_EXTENSION - 2;
    else if (first_frames > 1 && whole_used) return 5;
    else if (max_frames>=1 && p->buf_size < 10*max_framesizes) return 1;
    else                   return 0;
    //mpegps_mp3_unrecognized_format.mpg has max_frames=3
}
 
static void read_xing_toc(AVFormatContext *s, int64_t filesize, int64_t duration)
{
    int i;
    MP3DecContext *mp3 = s->priv_data;
    int fast_seek = s->flags & AVFMT_FLAG_FAST_SEEK;
    int fill_index = (mp3->usetoc || fast_seek) && duration > 0;
 
    if (!filesize &&
        (filesize = avio_size(s->pb)) <= 0) {
        av_log(s, AV_LOG_WARNING, "Cannot determine file size, skipping TOC table.\n");
        fill_index = 0;
        filesize = 0;
    }
 
    for (i = 0; i < XING_TOC_COUNT; i++) {
        uint8_t b = avio_r8(s->pb);
        if (fill_index)
            av_add_index_entry(s->streams[0],
                           av_rescale(b, filesize, 256),
                           av_rescale(i, duration, XING_TOC_COUNT),
                           0, 0, AVINDEX_KEYFRAME);
    }
    if (fill_index)
        mp3->xing_toc = 1;
}
 
static void mp3_parse_info_tag(AVFormatContext *s, AVStream *st,
                               MPADecodeHeader *c, uint32_t spf)
{
#define LAST_BITS(k, n) ((k) & ((1 << (n)) - 1))
#define MIDDLE_BITS(k, m, n) LAST_BITS((k) >> (m), ((n) - (m) + 1))
 
    FFStream *const sti = ffstream(st);
    uint16_t crc;
    uint32_t v;
 
    char version[10];
 
    uint32_t peak   = 0;
    int32_t  r_gain = INT32_MIN, a_gain = INT32_MIN;
 
    MP3DecContext *mp3 = s->priv_data;
    static const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
    uint64_t fsize = avio_size(s->pb);
    int64_t pos = avio_tell(s->pb);
    fsize = fsize >= pos ? fsize - pos : 0;
 
    /* Check for Xing / Info tag */
    avio_skip(s->pb, xing_offtbl[c->lsf == 1][c->nb_channels == 1]);
    v = avio_rb32(s->pb);
    mp3->is_cbr = v == MKBETAG('I', 'n', 'f', 'o');
    if (v != MKBETAG('X', 'i', 'n', 'g') && !mp3->is_cbr)
        return;
 
    v = avio_rb32(s->pb);
    if (v & XING_FLAG_FRAMES)
        mp3->frames = avio_rb32(s->pb);
    if (v & XING_FLAG_SIZE)
        mp3->header_filesize = avio_rb32(s->pb);
    if (fsize && mp3->header_filesize) {
        uint64_t min, delta;
        min = FFMIN(fsize, mp3->header_filesize);
        delta = FFMAX(fsize, mp3->header_filesize) - min;
        if (fsize > mp3->header_filesize && delta > min >> 4) {
            mp3->frames = 0;
            av_log(s, AV_LOG_WARNING,
                   "invalid concatenated file detected - using bitrate for duration\n");
        } else if (delta > min >> 4) {
            av_log(s, AV_LOG_WARNING,
                   "filesize and duration do not match (growing file?)\n");
        }
    }
    if (v & XING_FLAG_TOC)
        read_xing_toc(s, mp3->header_filesize, av_rescale_q(mp3->frames,
                                       (AVRational){spf, c->sample_rate},
                                       st->time_base));
    /* VBR quality */
    if (v & XING_FLAC_QSCALE)
        avio_rb32(s->pb);
 
    /* Encoder short version string */
    memset(version, 0, sizeof(version));
    avio_read(s->pb, version, 9);
 
    /* Info Tag revision + VBR method */
    avio_r8(s->pb);
 
    /* Lowpass filter value */
    avio_r8(s->pb);
 
    /* ReplayGain peak */
    v    = avio_rb32(s->pb);
    peak = av_rescale(v, 100000, 1 << 23);
 
    /* Radio ReplayGain */
    v = avio_rb16(s->pb);
 
    if (MIDDLE_BITS(v, 13, 15) == 1) {
        r_gain = MIDDLE_BITS(v, 0, 8) * 10000;
 
        if (v & (1 << 9))
            r_gain *= -1;
    }
 
    /* Audiophile ReplayGain */
    v = avio_rb16(s->pb);
 
    if (MIDDLE_BITS(v, 13, 15) == 2) {
        a_gain = MIDDLE_BITS(v, 0, 8) * 10000;
 
        if (v & (1 << 9))
            a_gain *= -1;
    }
 
    /* Encoding flags + ATH Type */
    avio_r8(s->pb);
 
    /* if ABR {specified bitrate} else {minimal bitrate} */
    avio_r8(s->pb);
 
    /* Encoder delays */
    v = avio_rb24(s->pb);
    if (AV_RB32(version) == MKBETAG('L', 'A', 'M', 'E')
        || AV_RB32(version) == MKBETAG('L', 'a', 'v', 'f')
        || AV_RB32(version) == MKBETAG('L', 'a', 'v', 'c')
    ) {
 
        mp3->start_pad = v>>12;
        mp3->  end_pad = v&4095;
        sti->start_skip_samples = mp3->start_pad + 528 + 1;
        if (mp3->frames) {
            sti->first_discard_sample = -mp3->end_pad + 528 + 1 + mp3->frames * (int64_t)spf;
            sti->last_discard_sample = mp3->frames * (int64_t)spf;
        }
        av_log(s, AV_LOG_DEBUG, "pad %d %d\n", mp3->start_pad, mp3->  end_pad);
    }
 
    /* Misc */
    avio_r8(s->pb);
 
    /* MP3 gain */
    avio_r8(s->pb);
 
    /* Preset and surround info */
    avio_rb16(s->pb);
 
    /* Music length */
    avio_rb32(s->pb);
 
    /* Music CRC */
    avio_rb16(s->pb);
 
    /* Info Tag CRC */
    crc = ffio_get_checksum(s->pb);
    v   = avio_rb16(s->pb);
 
    if (v == crc) {
        ff_replaygain_export_raw(st, r_gain, peak, a_gain, 0);
        av_dict_set(&st->metadata, "encoder", version, 0);
    }
}
 
static void mp3_parse_vbri_tag(AVFormatContext *s, AVStream *st, int64_t base)
{
    uint32_t v;
    MP3DecContext *mp3 = s->priv_data;
 
    /* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */
    avio_seek(s->pb, base + 4 + 32, SEEK_SET);
    v = avio_rb32(s->pb);
    if (v == MKBETAG('V', 'B', 'R', 'I')) {
        /* Check tag version */
        if (avio_rb16(s->pb) == 1) {
            /* skip delay and quality */
            avio_skip(s->pb, 4);
            mp3->header_filesize = avio_rb32(s->pb);
            mp3->frames = avio_rb32(s->pb);
        }
    }
}
 
/**
 * Look the iTunSMPB tag up under every key it can land on. A COMM frame keeps
 * its language in the key, and while Apple writes eng, anything that retags
 * the file is free to write its own, valid or not.
 *
 * The bare key is for files remuxed by versions that exposed a COMM descriptor
 * as a metadata key of its own: those wrote the tag back out as a TXXX frame,
 * which carries no language and is keyed by its description alone.
 */
static const AVDictionaryEntry *find_itunes_smpb(const AVDictionary *metadata)
{
    static const char comment[] = "comment-iTunSMPB";
    const AVDictionaryEntry *de = NULL;
 
    while ((de = av_dict_get(metadata, comment, de, AV_DICT_IGNORE_SUFFIX))) {
        const char *lang = de->key + sizeof(comment) - 1;
 
        /* und and xxx come without a suffix, the rest as a three letter one. */
        if (!*lang || (*lang == '-' && strlen(lang + 1) == 3))
            return de;
    }
 
    return av_dict_get(metadata, "iTunSMPB", NULL, 0);
}
 
/**
 * Parse the gapless playback information Apple encoders store in an iTunSMPB
 * comment instead of in the LAME extension of the Xing tag.
 */
static void mp3_parse_itunes_smpb(AVFormatContext *s, AVStream *st,
                                  const MPADecodeHeader *c, uint32_t spf)
{
    FFStream *const sti = ffstream(st);
    MP3DecContext *mp3 = s->priv_data;
    const AVDictionaryEntry *de;
    int64_t priming, remainder, samples;
 
    /* A LAME tag, if any, already described the padding. */
    if (sti->start_skip_samples)
        return;
 
    if (!(de = find_itunes_smpb(s->metadata)))
        return;
 
    if (ff_itunes_parse_smpb(de->value, &priming, &remainder, &samples) < 0)
        return;
 
    if (priming > 16384 || !samples)
        return;
 
    /* The three counts must add up to what the frames actually decode to. */
    if (mp3->frames &&
        priming + samples + remainder != mp3->frames * (int64_t)spf)
        return;
 
    /* Contrary to the LAME tag, the priming count covers the decoder delay. */
    sti->start_skip_samples   = priming;
    sti->first_discard_sample = priming + samples;
    sti->last_discard_sample  = priming + samples + remainder;
 
    st->duration = av_rescale_q(samples, (AVRational){ 1, c->sample_rate },
                                st->time_base);
}
 
/**
 * Try to find Xing/Info/VBRI tags and compute duration from info therein
 */
static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
{
    uint32_t v, spf;
    MPADecodeHeader c;
    int vbrtag_size = 0;
    MP3DecContext *mp3 = s->priv_data;
    int ret;
 
    ffio_init_checksum(s->pb, ff_crcA001_update, 0);
 
    v = avio_rb32(s->pb);
 
    ret = avpriv_mpegaudio_decode_header(&c, v);
    if (ret < 0)
        return ret;
    else if (ret == 0)
        vbrtag_size = c.frame_size;
    if (c.layer != 3)
        return -1;
 
    spf = c.lsf ? 576 : 1152; /* Samples per frame, layer 3 */
 
    mp3->frames = 0;
    mp3->header_filesize   = 0;
    mp3->frame_duration = av_rescale_q(spf, (AVRational){1, c.sample_rate}, st->time_base);
 
    mp3_parse_info_tag(s, st, &c, spf);
    mp3_parse_vbri_tag(s, st, base);
    mp3_parse_itunes_smpb(s, st, &c, spf);
 
    /* Packets keep the skipped samples, so shift the timeline instead. */
    if (ffstream(st)->start_skip_samples)
        st->start_time = av_rescale_q(ffstream(st)->start_skip_samples,
                                      (AVRational){1, c.sample_rate},
                                      st->time_base);
 
    if (!mp3->frames && !mp3->header_filesize)
        return -1;
 
    /* Skip the vbr tag frame */
    avio_seek(s->pb, base + vbrtag_size, SEEK_SET);
 
    if (mp3->frames) {
        int64_t full_duration_samples;
 
        full_duration_samples = mp3->frames * (int64_t)spf;
        if (st->duration == AV_NOPTS_VALUE)
            st->duration = av_rescale_q(full_duration_samples - mp3->start_pad - mp3->end_pad,
                                        (AVRational){1, c.sample_rate},
                                        st->time_base);
 
        if (mp3->header_filesize && !mp3->is_cbr)
            st->codecpar->bit_rate = av_rescale(mp3->header_filesize, 8 * c.sample_rate,
                                                full_duration_samples);
    }
 
    return 0;
}
 
static int mp3_read_header(AVFormatContext *s)
{
    FFFormatContext *const si = ffformatcontext(s);
    MP3DecContext *mp3 = s->priv_data;
    AVStream *st;
    FFStream *sti;
    int64_t off;
    int ret;
    int i;
 
    s->metadata = si->id3v2_meta;
    si->id3v2_meta = NULL;
 
    st = avformat_new_stream(s, NULL);
    if (!st)
        return AVERROR(ENOMEM);
    sti = ffstream(st);
 
    st->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
    st->codecpar->codec_id = AV_CODEC_ID_MP3;
    sti->need_parsing = AVSTREAM_PARSE_FULL_RAW;
    st->start_time = 0;
 
    // lcm of all mp3 sample rates
    avpriv_set_pts_info(st, 64, 1, 14112000);
 
    ffiocontext(s->pb)->maxsize = -1;
    off = avio_tell(s->pb);
 
    if (!av_dict_count(s->metadata))
        ff_id3v1_read(s);
 
    if (s->pb->seekable & AVIO_SEEKABLE_NORMAL)
        mp3->filesize = avio_size(s->pb);
 
    if (mp3_parse_vbr_tags(s, st, off) < 0)
        avio_seek(s->pb, off, SEEK_SET);
 
    ret = ff_replaygain_export(st, s->metadata);
    if (ret < 0)
        return ret;
 
    ret = ffio_ensure_seekback(s->pb, 64 * 1024 + MPA_MAX_CODED_FRAME_SIZE + 4);
    if (ret < 0)
        return ret;
 
    off = avio_tell(s->pb);
    for (i = 0; i < 64 * 1024; i++) {
        uint32_t header, header2;
        int frame_size;
        frame_size = check(s->pb, off + i, &header);
        if (frame_size > 0) {
            ret = check(s->pb, off + i + frame_size, &header2);
            if (ret >= 0 && (header & MP3_MASK) == (header2 & MP3_MASK))
                break;
        } else if (frame_size == CHECK_SEEK_FAILED) {
            av_log(s, AV_LOG_ERROR, "Failed to find two consecutive MPEG audio frames.\n");
            return AVERROR_INVALIDDATA;
        }
    }
    if (i == 64 * 1024) {
        off = avio_seek(s->pb, off, SEEK_SET);
    } else {
        av_log(s, i > 0 ? AV_LOG_INFO : AV_LOG_VERBOSE, "Skipping %d bytes of junk at %"PRId64".\n", i, off);
        off = avio_seek(s->pb, off + i, SEEK_SET);
    }
    if (off < 0)
        return off;
 
    // the seek index is relative to the end of the xing vbr headers
    for (int i = 0; i < sti->nb_index_entries; i++)
        sti->index_entries[i].pos += off;
 
    /* the parameters will be extracted from the compressed bitstream */
    return 0;
}
 
#define MP3_PACKET_SIZE 1024
 
static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    MP3DecContext *mp3 = s->priv_data;
    int ret, size;
    int64_t pos;
 
    size = MP3_PACKET_SIZE;
    pos = avio_tell(s->pb);
    if (mp3->filesize > ID3v1_TAG_SIZE && pos < mp3->filesize)
        size= FFMIN(size, mp3->filesize - pos);
 
    ret = av_get_packet(s->pb, pkt, size);
    if (ret <= 0) {
        if(ret<0)
            return ret;
        return AVERROR_EOF;
    }
 
    pkt->flags &= ~AV_PKT_FLAG_CORRUPT;
    pkt->stream_index = 0;
 
    return ret;
}
 
#define SEEK_WINDOW 4096
 
static int check(AVIOContext *pb, int64_t pos, uint32_t *ret_header)
{
    int64_t ret = avio_seek(pb, pos, SEEK_SET);
    uint8_t header_buf[4];
    unsigned header;
    MPADecodeHeader sd;
    if (ret < 0)
        return CHECK_SEEK_FAILED;
 
    ret = avio_read(pb, &header_buf[0], 4);
    /* We should always find four bytes for a valid mpa header. */
    if (ret < 4)
        return CHECK_SEEK_FAILED;
 
    header = AV_RB32(&header_buf[0]);
    if (ff_mpa_check_header(header) < 0)
        return CHECK_WRONG_HEADER;
    if (avpriv_mpegaudio_decode_header(&sd, header) == 1)
        return CHECK_WRONG_HEADER;
 
    if (ret_header)
        *ret_header = header;
    return sd.frame_size;
}
 
static int64_t mp3_sync(AVFormatContext *s, int64_t target_pos, int flags)
{
    int dir = (flags&AVSEEK_FLAG_BACKWARD) ? -1 : 1;
    int64_t best_pos;
    int best_score, i, j;
    int64_t ret;
 
    avio_seek(s->pb, FFMAX(target_pos - SEEK_WINDOW, 0), SEEK_SET);
    ret = avio_seek(s->pb, target_pos, SEEK_SET);
    if (ret < 0)
        return ret;
 
#define MIN_VALID 3
    best_pos = target_pos;
    best_score = 999;
    for (i = 0; i < SEEK_WINDOW; i++) {
        int64_t pos = target_pos + (dir > 0 ? i - SEEK_WINDOW/4 : -i);
        int64_t candidate = -1;
        int score = 999;
 
        if (pos < 0)
            continue;
 
        for (j = 0; j < MIN_VALID; j++) {
            ret = check(s->pb, pos, NULL);
            if (ret < 0) {
                if (ret == CHECK_WRONG_HEADER) {
                    break;
                } else if (ret == CHECK_SEEK_FAILED) {
                    av_log(s, AV_LOG_ERROR, "Could not seek to %"PRId64".\n", pos);
                    return AVERROR(EINVAL);
                }
            }
            if ((target_pos - pos)*dir <= 0 && FFABS(MIN_VALID/2-j) < score) {
                candidate = pos;
                score = FFABS(MIN_VALID/2-j);
            }
            pos += ret;
        }
        if (best_score > score && j == MIN_VALID) {
            best_pos = candidate;
            best_score = score;
            if(score == 0)
                break;
        }
    }
 
    return avio_seek(s->pb, best_pos, SEEK_SET);
}
 
static int mp3_seek(AVFormatContext *s, int stream_index, int64_t timestamp,
                    int flags)
{
    FFFormatContext *const si = ffformatcontext(s);
    MP3DecContext *mp3 = s->priv_data;
    AVIndexEntry *ie, ie1;
    AVStream *st = s->streams[0];
    FFStream *const sti = ffstream(st);
    int64_t best_pos;
    int fast_seek = s->flags & AVFMT_FLAG_FAST_SEEK;
    int64_t filesize = mp3->header_filesize;
 
    if (filesize <= 0) {
        int64_t size = avio_size(s->pb);
        if (size > 0 && size > si->data_offset)
            filesize = size - si->data_offset;
    }
 
    if (mp3->xing_toc && (mp3->usetoc || (fast_seek && !mp3->is_cbr))) {
        int64_t ret = av_index_search_timestamp(st, timestamp, flags);
 
        // NOTE: The MP3 TOC is not a precise lookup table. Accuracy is worse
        // for bigger files.
        av_log(s, AV_LOG_WARNING, "Using MP3 TOC to seek; may be imprecise.\n");
 
        if (ret < 0)
            return ret;
 
        ie = &sti->index_entries[ret];
    } else if (fast_seek && st->duration > 0 && filesize > 0) {
        if (!mp3->is_cbr)
            av_log(s, AV_LOG_WARNING, "Using scaling to seek VBR MP3; may be imprecise.\n");
 
        ie = &ie1;
        timestamp = av_clip64(timestamp, 0, st->duration);
        ie->timestamp = timestamp;
        ie->pos       = av_rescale(timestamp, filesize, st->duration) + si->data_offset;
    } else {
        return -1; // generic index code
    }
 
    best_pos = mp3_sync(s, ie->pos, flags);
    if (best_pos < 0)
        return best_pos;
 
    if (mp3->is_cbr && ie == &ie1 && mp3->frames && mp3->header_filesize > 0) {
        ie1.timestamp = mp3->frame_duration * av_rescale(best_pos - si->data_offset, mp3->frames, mp3->header_filesize);
    }
 
    avpriv_update_cur_dts(s, st, ie->timestamp);
    return 0;
}
 
static const AVOption options[] = {
    { "usetoc", "use table of contents", offsetof(MP3DecContext, usetoc), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, AV_OPT_FLAG_DECODING_PARAM},
    { NULL },
};
 
static const AVClass demuxer_class = {
    .class_name = "mp3",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
    .category   = AV_CLASS_CATEGORY_DEMUXER,
};
 
const FFInputFormat ff_mp3_demuxer = {
    .p.name         = "mp3",
    .p.long_name    = NULL_IF_CONFIG_SMALL("MP2/3 (MPEG audio layer 2/3)"),
    .p.flags        = AVFMT_GENERIC_INDEX,
    .p.extensions   = "mp2,mp3,m2a,mpa", /* XXX: use probe */
    .p.priv_class   = &demuxer_class,
    .p.mime_type    = "audio/mpeg",
    .flags_internal = FF_INFMT_FLAG_ID3V2_AUTO,
    .read_probe     = mp3_read_probe,
    .read_header    = mp3_read_header,
    .read_packet    = mp3_read_packet,
    .read_seek      = mp3_seek,
    .priv_data_size = sizeof(MP3DecContext),
};