+/*
+ * Add a frame to XING data.
+ * Following lame's "VbrTag.c".
+ */
+static void mp3_xing_add_frame(MP3Context *mp3, AVPacket *pkt)
+{
+ int i;
+
+ mp3->frames++;
+ mp3->seen++;
+ mp3->size += pkt->size;
+
+ if (mp3->want == mp3->seen) {
+ mp3->bag[mp3->pos] = mp3->size;
+
+ if (XING_NUM_BAGS == ++mp3->pos) {
+ /* shrink table to half size by throwing away each second bag. */
+ for (i = 1; i < XING_NUM_BAGS; i += 2)
+ mp3->bag[i / 2] = mp3->bag[i];
+
+ /* double wanted amount per bag. */
+ mp3->want *= 2;
+ /* adjust current position to half of table size. */
+ mp3->pos = XING_NUM_BAGS / 2;
+ }
+
+ mp3->seen = 0;
+ }
+}
+
+static int mp3_write_audio_packet(AVFormatContext *s, AVPacket *pkt)
+{
+ MP3Context *mp3 = s->priv_data;
+
+ if (mp3->xing_offset && pkt->size >= 4) {
+ MPADecodeHeader c;
+
+ avpriv_mpegaudio_decode_header(&c, AV_RB32(pkt->data));
+
+ if (!mp3->initial_bitrate)
+ mp3->initial_bitrate = c.bit_rate;
+ if ((c.bit_rate == 0) || (mp3->initial_bitrate != c.bit_rate))
+ mp3->has_variable_bitrate = 1;
+
+ mp3_xing_add_frame(mp3, pkt);
+ }
+
+ return ff_raw_write_packet(s, pkt);
+}
+