[FFmpeg-devel] [PATCH 2/2] avformat: parse iTunes gapless information

[kode54 at gmail.com]

From: Chris Moeller <kode54 at gmail.com>

---
 libavformat/mp3dec.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
index 56c7f8c..3055e2c 100644
--- a/libavformat/mp3dec.c
+++ b/libavformat/mp3dec.c
@@ -295,6 +295,53 @@ 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;
+    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;
+
+    if (sscanf(de->value, "%x %x %x %llx %x %llx", &zero, &start_pad, &end_pad, duration, &zero, &last_eight_frames_offset) < 6) {
+        *duration = 0;
+        return;
+    }
+
+    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;
+    avio_seek(s->pb, base + vbrtag_size + last_eight_frames_offset, SEEK_SET);
+    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 +350,10 @@ 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 +376,29 @@ 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;
 }
-- 
2.7.4 (Apple Git-66)