static void mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base) { uint32_t v, spf; int frames = -1; /* Total number of frames in file */ const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}}; MPADecodeContext c; v = get_be32(s->pb); if(ff_mpa_check_header(v) < 0) return; ff_mpegaudio_decode_header(&c, v); if(c.layer != 3) return; /* Check for Xing / Info tag */ url_fseek(s->pb, xing_offtbl[c.lsf == 1][c.nb_channels == 1], SEEK_CUR); v = get_be32(s->pb); if(v == MKBETAG('X', 'i', 'n', 'g') || v == MKBETAG('I', 'n', 'f', 'o')) { v = get_be32(s->pb); if(v & 0x1) frames = get_be32(s->pb); } /* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */ url_fseek(s->pb, base + 4 + 32, SEEK_SET); v = get_be32(s->pb); if(v == MKBETAG('V', 'B', 'R', 'I')) { /* Check tag version */ if(get_be16(s->pb) == 1) { /* skip delay, quality and total bytes */ url_fseek(s->pb, 8, SEEK_CUR); frames = get_be32(s->pb); } } if(frames < 0) return; spf = c.lsf ? 576 : 1152; /* Samples per frame, layer 3 */ st->duration = av_rescale_q(frames, (AVRational){spf, c.sample_rate}, st->time_base); }