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ffmpeg / libavformat / mp3dec.c @ b7effd4e

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/*
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 * MP3 demuxer
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 * Copyright (c) 2003 Fabrice Bellard
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 *
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 * This file is part of FFmpeg.
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 *
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 * FFmpeg is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * FFmpeg is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with FFmpeg; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include "libavutil/avstring.h"
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#include "libavutil/intreadwrite.h"
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#include "avformat.h"
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#include "id3v2.h"
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#include "id3v1.h"
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#include "libavcodec/mpegaudiodecheader.h"
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/* mp3 read */
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static int mp3_read_probe(AVProbeData *p)
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{
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    int max_frames, first_frames = 0;
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    int fsize, frames, sample_rate;
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    uint32_t header;
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    uint8_t *buf, *buf0, *buf2, *end;
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    AVCodecContext avctx;
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    buf0 = p->buf;
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    end = p->buf + p->buf_size - sizeof(uint32_t);
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    while(buf0 < end && !*buf0)
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        buf0++;
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    max_frames = 0;
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    buf = buf0;
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    for(; buf < end; buf= buf2+1) {
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        buf2 = buf;
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        for(frames = 0; buf2 < end; frames++) {
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            header = AV_RB32(buf2);
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            fsize = ff_mpa_decode_header(&avctx, header, &sample_rate, &sample_rate, &sample_rate, &sample_rate);
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            if(fsize < 0)
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                break;
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            buf2 += fsize;
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        }
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        max_frames = FFMAX(max_frames, frames);
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        if(buf == buf0)
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            first_frames= frames;
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    }
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    // keep this in sync with ac3 probe, both need to avoid
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    // issues with MPEG-files!
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    if   (first_frames>=4) return AVPROBE_SCORE_MAX/2+1;
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    else if(max_frames>500)return AVPROBE_SCORE_MAX/2;
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    else if(max_frames>=4) return AVPROBE_SCORE_MAX/4;
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    else if(max_frames>=1) return 1;
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    else                   return 0;
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//mpegps_mp3_unrecognized_format.mpg has max_frames=3
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}
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/**
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 * Try to find Xing/Info/VBRI tags and compute duration from info therein
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 */
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static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
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{
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    uint32_t v, spf;
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    unsigned frames = 0; /* Total number of frames in file */
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    unsigned size = 0; /* Total number of bytes in the stream */
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    const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
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    MPADecodeHeader c;
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    int vbrtag_size = 0;
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    v = avio_rb32(s->pb);
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    if(ff_mpa_check_header(v) < 0)
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      return -1;
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    if (ff_mpegaudio_decode_header(&c, v) == 0)
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        vbrtag_size = c.frame_size;
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    if(c.layer != 3)
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        return -1;
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    /* Check for Xing / Info tag */
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    url_fseek(s->pb, xing_offtbl[c.lsf == 1][c.nb_channels == 1], SEEK_CUR);
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    v = avio_rb32(s->pb);
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    if(v == MKBETAG('X', 'i', 'n', 'g') || v == MKBETAG('I', 'n', 'f', 'o')) {
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        v = avio_rb32(s->pb);
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        if(v & 0x1)
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            frames = avio_rb32(s->pb);
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        if(v & 0x2)
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            size = avio_rb32(s->pb);
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    }
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    /* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */
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    url_fseek(s->pb, base + 4 + 32, SEEK_SET);
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    v = avio_rb32(s->pb);
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    if(v == MKBETAG('V', 'B', 'R', 'I')) {
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        /* Check tag version */
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        if(avio_rb16(s->pb) == 1) {
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            /* skip delay and quality */
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            url_fseek(s->pb, 4, SEEK_CUR);
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            frames = avio_rb32(s->pb);
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            size = avio_rb32(s->pb);
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        }
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    }
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    if(!frames && !size)
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        return -1;
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    /* Skip the vbr tag frame */
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    url_fseek(s->pb, base + vbrtag_size, SEEK_SET);
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    spf = c.lsf ? 576 : 1152; /* Samples per frame, layer 3 */
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    if(frames)
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        st->duration = av_rescale_q(frames, (AVRational){spf, c.sample_rate},
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                                    st->time_base);
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    if(size && frames)
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        st->codec->bit_rate = av_rescale(size, 8 * c.sample_rate, frames * (int64_t)spf);
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    return 0;
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}
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static int mp3_read_header(AVFormatContext *s,
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                           AVFormatParameters *ap)
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{
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    AVStream *st;
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    int64_t off;
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    st = av_new_stream(s, 0);
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    if (!st)
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        return AVERROR(ENOMEM);
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    st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
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    st->codec->codec_id = CODEC_ID_MP3;
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    st->need_parsing = AVSTREAM_PARSE_FULL;
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    st->start_time = 0;
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    // lcm of all mp3 sample rates
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    av_set_pts_info(st, 64, 1, 14112000);
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    off = url_ftell(s->pb);
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    if (!av_metadata_get(s->metadata, "", NULL, AV_METADATA_IGNORE_SUFFIX))
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        ff_id3v1_read(s);
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    if (mp3_parse_vbr_tags(s, st, off) < 0)
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        url_fseek(s->pb, off, SEEK_SET);
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    /* the parameters will be extracted from the compressed bitstream */
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    return 0;
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}
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#define MP3_PACKET_SIZE 1024
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static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt)
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{
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    int ret, size;
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    //    AVStream *st = s->streams[0];
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    size= MP3_PACKET_SIZE;
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    ret= av_get_packet(s->pb, pkt, size);
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    pkt->stream_index = 0;
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    if (ret <= 0) {
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        return AVERROR(EIO);
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    }
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    if (ret > ID3v1_TAG_SIZE &&
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        memcmp(&pkt->data[ret - ID3v1_TAG_SIZE], "TAG", 3) == 0)
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        ret -= ID3v1_TAG_SIZE;
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    /* note: we need to modify the packet size here to handle the last
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       packet */
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    pkt->size = ret;
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    return ret;
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}
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AVInputFormat ff_mp3_demuxer = {
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    "mp3",
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    NULL_IF_CONFIG_SMALL("MPEG audio layer 2/3"),
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    0,
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    mp3_read_probe,
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    mp3_read_header,
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    mp3_read_packet,
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    .flags= AVFMT_GENERIC_INDEX,
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    .extensions = "mp2,mp3,m2a", /* XXX: use probe */
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};