[FFmpeg-devel] [PATCH] avformat: parse iTunes gapless information

wm4 nfxjfg at googlemail.com
Fri Jan 27 14:10:39 EET 2017


On Thu, 26 Jan 2017 16:47:12 -0800
Christopher Snowhill <kode54 at gmail.com> wrote:

> Signed-off-by: Christopher Snowhill <kode54 at gmail.com>
> ---
>  libavformat/mp3dec.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 76 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
> index 099ca57..b895e37 100644
> --- a/libavformat/mp3dec.c
> +++ b/libavformat/mp3dec.c
> @@ -295,6 +295,66 @@ static void mp3_parse_vbri_tag(AVFormatContext *s, AVStream *st, int64_t base)
>      }
>  }
>  
> +static void mp3_parse_itunes_tag(AVFormatContext *s, AVStream *st, MPADecodeHeader *c, int64_t base, int vbrtag_size, unsigned int *size, uint64_t *duration)
> +{
> +    uint32_t v;
> +    AVDictionaryEntry *de;
> +    MP3DecContext *mp3 = s->priv_data;
> +    size_t length;
> +    uint32_t zero, start_pad, end_pad;
> +    uint64_t last_eight_frames_offset;
> +    int64_t temp_duration, file_size;
> +    int i;
> +
> +    if (!s->metadata || !(de = av_dict_get(s->metadata, "iTunSMPB", NULL, 0)))
> +        return;
> +
> +    length = strlen(de->value);
> +
> +    /* Minimum length is one digit per field plus the whitespace, maximum length should depend on field type
> +     * There are four fields we need in the first six, the rest are currently zero padding */
> +    if (length < (12 + 11) || length > (10 * 8 + 2 * 16 + 11))
> +        return;
> +
> +    file_size = avio_size(s->pb);
> +    if (file_size < 0)
> +        file_size = 0;
> +
> +    if (sscanf(de->value, "%"PRIx32" %"PRIx32" %"PRIx32" %"PRIx64" %"PRIx32" %"PRIx64, &zero, &start_pad, &end_pad, &temp_duration, &zero, &last_eight_frames_offset) < 6 ||
> +        temp_duration < 0 ||
> +        start_pad > (576 * 2 * 32) ||
> +        end_pad > (576 * 2 * 64) ||
> +        (file_size && (last_eight_frames_offset >= (file_size - base - vbrtag_size)))) {
> +        *duration = 0;
> +        return;
> +    }
> +
> +    *duration = temp_duration;
> +
> +    mp3->start_pad = start_pad;
> +    mp3->end_pad = end_pad;
> +    if (end_pad >= 528 + 1)
> +        mp3->end_pad = end_pad - (528 + 1);
> +    st->start_skip_samples = mp3->start_pad + 528 + 1;
> +    av_log(s, AV_LOG_DEBUG, "pad %d %d\n", mp3->start_pad, mp3->end_pad);
> +    if (!s->pb->seekable)
> +        return;
> +
> +    *size = (unsigned int) last_eight_frames_offset;
> +    if (avio_seek(s->pb, base + vbrtag_size + last_eight_frames_offset, SEEK_SET) < 0)
> +        return;
> +
> +    for (i = 0; i < 8; i++) {
> +        v = avio_rb32(s->pb);
> +        if (ff_mpa_check_header(v) < 0)
> +            return;
> +        if (avpriv_mpegaudio_decode_header(c, v) != 0)
> +            break;
> +        *size += c->frame_size;
> +        avio_skip(s->pb, c->frame_size - 4);
> +    }
> +}
> +
>  /**
>   * Try to find Xing/Info/VBRI tags and compute duration from info therein
>   */
> @@ -303,8 +363,10 @@ static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
>      uint32_t v, spf;
>      MPADecodeHeader c;
>      int vbrtag_size = 0;
> +    unsigned int size = 0;
>      MP3DecContext *mp3 = s->priv_data;
>      int ret;
> +    uint64_t duration = 0;
>  
>      ffio_init_checksum(s->pb, ff_crcA001_update, 0);
>  
> @@ -327,16 +389,29 @@ static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
>      mp3_parse_vbri_tag(s, st, base);
>  
>      if (!mp3->frames && !mp3->header_filesize)
> +        vbrtag_size = 0;
> +
> +    mp3_parse_itunes_tag(s, st, &c, base, vbrtag_size, &size, &duration);
> +
> +    if (!mp3->frames && !size && !duration)
>          return -1;
>  
>      /* Skip the vbr tag frame */
>      avio_seek(s->pb, base + vbrtag_size, SEEK_SET);
>  
> -    if (mp3->frames)
> +    if (duration)
> +        st->duration = av_rescale_q(duration, (AVRational){1, c.sample_rate}, st->time_base);
> +    else if (mp3->frames)
>          st->duration = av_rescale_q(mp3->frames, (AVRational){spf, c.sample_rate},
>                                      st->time_base);
>      if (mp3->header_filesize && mp3->frames && !mp3->is_cbr)
>          st->codecpar->bit_rate = av_rescale(mp3->header_filesize, 8 * c.sample_rate, mp3->frames * (int64_t)spf);
> +    if (size) {
> +        if (duration)
> +            st->codecpar->bit_rate = av_rescale(size, 8 * c.sample_rate, duration);
> +        else if (mp3->frames)
> +            st->codecpar->bit_rate = av_rescale(size, 8 * c.sample_rate, mp3->frames * (int64_t)spf);
> +    }
>  
>      return 0;
>  }

If we add this, can we add a fate sample as well? The test should be
similar to the other gapless tests.


More information about the ffmpeg-devel mailing list