mp3.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

static void id3v1_get_string(char *str, int str_size,
                             const uint8_t *buf, int buf_size)
{
    int i, c;
    char *q;

    q = str;
    for(i = 0; i < buf_size; i++) {
        c = buf[i];
        if (c == '\0')
            break;
        if ((q - str) >= str_size - 1)
            break;
        *q++ = c;
    }
    *q = '\0';
}

/* 'buf' must be ID3v1_TAG_SIZE byte long */
static int id3v1_parse_tag(AVFormatContext *s, const uint8_t *buf)
{
    char str[5];
    int genre;

    if (!(buf[0] == 'T' &&
          buf[1] == 'A' &&
          buf[2] == 'G'))
        return -1;
    id3v1_get_string(s->title, sizeof(s->title), buf + 3, 30);
    id3v1_get_string(s->author, sizeof(s->author), buf + 33, 30);
    id3v1_get_string(s->album, sizeof(s->album), buf + 63, 30);
    id3v1_get_string(str, sizeof(str), buf + 93, 4);
    s->year = atoi(str);
    id3v1_get_string(s->comment, sizeof(s->comment), buf + 97, 30);
    if (buf[125] == 0 && buf[126] != 0)
        s->track = buf[126];
    genre = buf[127];
    if (genre <= ID3v1_GENRE_MAX)
        av_strlcpy(s->genre, id3v1_genre_str[genre], sizeof(s->genre));
    return 0;
}

static void id3v1_create_tag(AVFormatContext *s, uint8_t *buf)
{
    int v, i;

    memset(buf, 0, ID3v1_TAG_SIZE); /* fail safe */
    buf[0] = 'T';
    buf[1] = 'A';
    buf[2] = 'G';
    strncpy(buf + 3, s->title, 30);
    strncpy(buf + 33, s->author, 30);
    strncpy(buf + 63, s->album, 30);
    v = s->year;
    if (v > 0) {
        for(i = 0;i < 4; i++) {
            buf[96 - i] = '0' + (v % 10);
            v = v / 10;
        }
    }
    strncpy(buf + 97, s->comment, 30);
    if (s->track != 0) {
        buf[125] = 0;
        buf[126] = s->track;
    }
    for(i = 0; i <= ID3v1_GENRE_MAX; i++) {
        if (!strcasecmp(s->genre, id3v1_genre_str[i])) {
            buf[127] = i;
            break;
        }
    }
}

/* mp3 read */

static int mp3_read_probe(AVProbeData *p)
{
    int max_frames, first_frames = 0;
    int fsize, frames, sample_rate;
    uint32_t header;
    uint8_t *buf, *buf2, *end;
    AVCodecContext avctx;

    if(id3v2_match(p->buf))
        return AVPROBE_SCORE_MAX/2+1; // this must be less than mpeg-ps because some retards put id3v2 tags before mpeg-ps files

    max_frames = 0;
    buf = p->buf;
    end = buf + FFMIN(4096, p->buf_size - sizeof(uint32_t));

    for(; buf < end; buf++) {
        buf2 = buf;

        for(frames = 0; buf2 < end; frames++) {
            header = AV_RB32(buf2);
            fsize = ff_mpa_decode_header(&avctx, header, &sample_rate);
            if(fsize < 0)
                break;
            buf2 += fsize;
        }
        max_frames = FFMAX(max_frames, frames);
        if(buf == p->buf)
            first_frames= frames;
    }
    if   (first_frames>=3) return AVPROBE_SCORE_MAX/2+1;
    else if(max_frames>=3) return AVPROBE_SCORE_MAX/4;
    else if(max_frames>=1) return 1;
    else                   return 0;
}

static int mp3_read_header(AVFormatContext *s,
                           AVFormatParameters *ap)
{
    AVStream *st;
    uint8_t buf[ID3v1_TAG_SIZE];
    int len, ret, filesize;

    st = av_new_stream(s, 0);
    if (!st)
        return AVERROR(ENOMEM);

    st->codec->codec_type = CODEC_TYPE_AUDIO;
    st->codec->codec_id = CODEC_ID_MP3;
    st->need_parsing = AVSTREAM_PARSE_FULL;

    /* try to get the TAG */
    if (!url_is_streamed(&s->pb)) {
        /* XXX: change that */
        filesize = url_fsize(&s->pb);
        if (filesize > 128) {
            url_fseek(&s->pb, filesize - 128, SEEK_SET);
            ret = get_buffer(&s->pb, buf, ID3v1_TAG_SIZE);
            if (ret == ID3v1_TAG_SIZE) {
                id3v1_parse_tag(s, buf);
            }
            url_fseek(&s->pb, 0, SEEK_SET);
        }
    }

    /* if ID3v2 header found, skip it */
    ret = get_buffer(&s->pb, buf, ID3v2_HEADER_SIZE);
    if (ret != ID3v2_HEADER_SIZE)
        return -1;
    if (id3v2_match(buf)) {
        /* parse ID3v2 header */
        len = ((buf[6] & 0x7f) << 21) |
            ((buf[7] & 0x7f) << 14) |
            ((buf[8] & 0x7f) << 7) |
            (buf[9] & 0x7f);
        id3v2_parse(s, len, buf[3], buf[5]);
    } else {
        url_fseek(&s->pb, 0, SEEK_SET);
    }

    /* 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)
{
    int ret, size;
    //    AVStream *st = s->streams[0];

    size= MP3_PACKET_SIZE;

    ret= av_get_packet(&s->pb, pkt, size);

    pkt->stream_index = 0;
    if (ret <= 0) {
        return AVERROR(EIO);
    }
    /* note: we need to modify the packet size here to handle the last
       packet */
    pkt->size = ret;
    return ret;
}

static int mp3_read_close(AVFormatContext *s)
{
    return 0;
}

#ifdef CONFIG_MUXERS
/* simple formats */

static void id3v2_put_size(AVFormatContext *s, int size)
{
    put_byte(&s->pb, size >> 21 & 0x7f);
    put_byte(&s->pb, size >> 14 & 0x7f);
    put_byte(&s->pb, size >> 7  & 0x7f);
    put_byte(&s->pb, size       & 0x7f);
}

static void id3v2_put_ttag(AVFormatContext *s, char *string, uint32_t tag)
{
    int len = strlen(string);
    put_be32(&s->pb, tag);
    id3v2_put_size(s, len + 1);
    put_be16(&s->pb, 0);
    put_byte(&s->pb, 3); /* UTF-8 */
    put_buffer(&s->pb, string, len);
}


/**
 * Write an ID3v2.4 header at beginning of stream
 */

static int mp3_write_header(struct AVFormatContext *s)
{
    int totlen = 0;
    char tracktxt[10];

    if(s->track)
        snprintf(tracktxt, sizeof(tracktxt) - 1, "%d", s->track);

    if(s->title[0])     totlen += 11 + strlen(s->title);
    if(s->author[0])    totlen += 11 + strlen(s->author);
    if(s->album[0])     totlen += 11 + strlen(s->album);
    if(s->genre[0])     totlen += 11 + strlen(s->genre);
    if(s->copyright[0]) totlen += 11 + strlen(s->copyright);
    if(s->track)        totlen += 11 + strlen(tracktxt);
    if(!(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT))
        totlen += strlen(LIBAVFORMAT_IDENT) + 11;

    if(totlen == 0)
        return 0;

    put_be32(&s->pb, MKBETAG('I', 'D', '3', 0x04)); /* ID3v2.4 */
    put_byte(&s->pb, 0);
    put_byte(&s->pb, 0); /* flags */

    id3v2_put_size(s, totlen);

    if(s->title[0])     id3v2_put_ttag(s, s->title,     MKBETAG('T', 'I', 'T', '2'));
    if(s->author[0])    id3v2_put_ttag(s, s->author,    MKBETAG('T', 'P', 'E', '1'));
    if(s->album[0])     id3v2_put_ttag(s, s->album,     MKBETAG('T', 'A', 'L', 'B'));
    if(s->genre[0])     id3v2_put_ttag(s, s->genre,     MKBETAG('T', 'C', 'O', 'N'));
    if(s->copyright[0]) id3v2_put_ttag(s, s->copyright, MKBETAG('T', 'C', 'O', 'P'));
    if(s->track)        id3v2_put_ttag(s, tracktxt,     MKBETAG('T', 'R', 'C', 'K'));
    if(!(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT))
        id3v2_put_ttag(s, LIBAVFORMAT_IDENT,            MKBETAG('T', 'E', 'N', 'C'));
    return 0;
}

static int mp3_write_packet(struct AVFormatContext *s, AVPacket *pkt)
{
    put_buffer(&s->pb, pkt->data, pkt->size);
    put_flush_packet(&s->pb);
    return 0;
}

static int mp3_write_trailer(struct AVFormatContext *s)
{
    uint8_t buf[ID3v1_TAG_SIZE];

    /* write the id3v1 tag */
    if (s->title[0] != '\0') {
        id3v1_create_tag(s, buf);
        put_buffer(&s->pb, buf, ID3v1_TAG_SIZE);
        put_flush_packet(&s->pb);
    }
    return 0;
}
#endif //CONFIG_MUXERS

#ifdef CONFIG_MP3_DEMUXER
AVInputFormat mp3_demuxer = {
    "mp3",
    "MPEG audio",
    0,
    mp3_read_probe,
    mp3_read_header,
    mp3_read_packet,
    mp3_read_close,
    .flags= AVFMT_GENERIC_INDEX,
    .extensions = "mp2,mp3,m2a", /* XXX: use probe */
};
#endif
#ifdef CONFIG_MP2_MUXER
AVOutputFormat mp2_muxer = {
    "mp2",
    "MPEG audio layer 2",
    "audio/x-mpeg",
#ifdef CONFIG_LIBMP3LAME
    "mp2,m2a",
#else
    "mp2,mp3,m2a",
#endif
    0,
    CODEC_ID_MP2,
    0,
    NULL,
    mp3_write_packet,
    mp3_write_trailer,
};
#endif
#ifdef CONFIG_MP3_MUXER
AVOutputFormat mp3_muxer = {
    "mp3",
    "MPEG audio layer 3",
    "audio/x-mpeg",
    "mp3",
    0,
    CODEC_ID_MP3,
    0,
    mp3_write_header,
    mp3_write_packet,
    mp3_write_trailer,
};
#endif