mp3enc: write Xing TOC

Based on the code by:
Peter Belkner <pbelkner@snafu.de>,
Michael Niedermayer <michaelni@gmx.at>,
Clément Bœsch <clement.boesch@smartjog.com>,
Reimar Döffinger <Reimar.Doeffinger@gmx.de>, and
Tobias Rapp <t.rapp@noa-audio.com>
Alex Converse <alex.converse@gmail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavformat/mp3enc.c

@@ -74,12 +74,27 @@ static int id3v1_create_tag(AVFormatContext *s, uint8_t *buf)
     return count;
 }
 
+#define XING_NUM_BAGS 400
+#define XING_TOC_SIZE 100
+// maximum size of the xing frame: offset/Xing/flags/frames/size/TOC
+#define XING_MAX_SIZE (32 + 4 + 4 + 4 + 4 + XING_TOC_SIZE)
+
 typedef struct MP3Context {
     const AVClass *class;
     ID3v2EncContext id3;
     int id3v2_version;
     int write_id3v1;
-    int64_t nb_frames_offset;
+
+    /* xing header */
+    int64_t xing_offset;
+    int32_t frames;
+    int32_t size;
+    uint32_t want;
+    uint32_t seen;
+    uint32_t pos;
+    uint64_t bag[XING_NUM_BAGS];
+    int initial_bitrate;
+    int has_variable_bitrate;
 
     /* index of the audio stream */
     int audio_stream_idx;
@@ -92,15 +107,17 @@ typedef struct MP3Context {
 
 static const uint8_t xing_offtbl[2][2] = {{32, 17}, {17, 9}};
 
-/* insert a dummy frame containing number of frames */
+/*
+ * Write an empty XING header and initialize respective data.
+ */
 static void mp3_write_xing(AVFormatContext *s)
 {
     MP3Context       *mp3 = s->priv_data;
     AVCodecContext *codec = s->streams[mp3->audio_stream_idx]->codec;
-    int       bitrate_idx = 1;    // 32 kbps
     int32_t        header;
     MPADecodeHeader  mpah;
     int srate_idx, i, channels;
+    int bitrate_idx;
     int xing_offset;
     int ver = 0;
 
@@ -132,6 +149,9 @@ static void mp3_write_xing(AVFormatContext *s)
              return;
     }
 
+    /* 64 kbps frame, should be large enough */
+    bitrate_idx = (ver == 3) ? 5 : 8;
+
     /* dummy MPEG audio header */
     header  =  0xff                                  << 24; // sync
     header |= (0x7 << 5 | ver << 3 | 0x1 << 1 | 0x1) << 16; // sync/audio-version/layer 3/no crc*/
@@ -141,17 +161,78 @@ static void mp3_write_xing(AVFormatContext *s)
 
     avpriv_mpegaudio_decode_header(&mpah, header);
 
+    av_assert0(mpah.frame_size >= XING_MAX_SIZE);
+
     xing_offset = xing_offtbl[ver != 3][codec->channels == 1];
     ffio_fill(s->pb, 0, xing_offset);
+    mp3->xing_offset = avio_tell(s->pb);
     ffio_wfourcc(s->pb, "Xing");
-    avio_wb32(s->pb, 0x1);    // only number of frames
-    mp3->nb_frames_offset = avio_tell(s->pb);
-    avio_wb32(s->pb, 0);
+    avio_wb32(s->pb, 0x01 | 0x02 | 0x04);  // frames / size / TOC
 
-    mpah.frame_size -= 4 + xing_offset + 4 + 4 + 4;
+    mp3->size = mpah.frame_size;
+    mp3->want = 1;
+
+    avio_wb32(s->pb, 0);  // frames
+    avio_wb32(s->pb, 0);  // size
+
+    // TOC
+    for (i = 0; i < XING_TOC_SIZE; i++)
+        avio_w8(s->pb, 255 * i / XING_TOC_SIZE);
+
+    mpah.frame_size -= 4 + xing_offset + 4 + 4 + 4 + 4 + XING_TOC_SIZE;
     ffio_fill(s->pb, 0, mpah.frame_size);
 }
 
+/*
+ * 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);
+}
+
 static int mp3_queue_flush(AVFormatContext *s)
 {
     MP3Context *mp3 = s->priv_data;
@@ -162,7 +243,7 @@ static int mp3_queue_flush(AVFormatContext *s)
     mp3_write_xing(s);
 
     while ((pktl = mp3->queue)) {
-        if (write && (ret = ff_raw_write_packet(s, &pktl->pkt)) < 0)
+        if (write && (ret = mp3_write_audio_packet(s, &pktl->pkt)) < 0)
             write = 0;
         av_free_packet(&pktl->pkt);
         mp3->queue = pktl->next;
@@ -172,30 +253,50 @@ static int mp3_queue_flush(AVFormatContext *s)
     return ret;
 }
 
+static void mp3_update_xing(AVFormatContext *s)
+{
+    MP3Context  *mp3 = s->priv_data;
+    int i;
+
+    /* replace "Xing" identification string with "Info" for CBR files. */
+    if (!mp3->has_variable_bitrate) {
+        avio_seek(s->pb, mp3->xing_offset, SEEK_SET);
+        ffio_wfourcc(s->pb, "Info");
+    }
+
+    avio_seek(s->pb, mp3->xing_offset + 8, SEEK_SET);
+    avio_wb32(s->pb, mp3->frames);
+    avio_wb32(s->pb, mp3->size);
+
+    avio_w8(s->pb, 0);  // first toc entry has to be zero.
+
+    for (i = 1; i < XING_TOC_SIZE; ++i) {
+        int j = i * mp3->pos / XING_TOC_SIZE;
+        int seek_point = 256LL * mp3->bag[j] / mp3->size;
+        avio_w8(s->pb, FFMIN(seek_point, 255));
+    }
+
+    avio_seek(s->pb, 0, SEEK_END);
+}
+
 static int mp3_write_trailer(struct AVFormatContext *s)
 {
     uint8_t buf[ID3v1_TAG_SIZE];
     MP3Context *mp3 = s->priv_data;
 
-    if (mp3 && mp3->pics_to_write) {
+    if (mp3->pics_to_write) {
         av_log(s, AV_LOG_WARNING, "No packets were sent for some of the "
                "attached pictures.\n");
         mp3_queue_flush(s);
     }
 
     /* write the id3v1 tag */
-    if (mp3 && mp3->write_id3v1 && id3v1_create_tag(s, buf) > 0) {
+    if (mp3->write_id3v1 && id3v1_create_tag(s, buf) > 0) {
         avio_write(s->pb, buf, ID3v1_TAG_SIZE);
     }
 
-    /* write number of frames */
-    if (mp3 && mp3->nb_frames_offset) {
-        avio_seek(s->pb, mp3->nb_frames_offset, SEEK_SET);
-        avio_wb32(s->pb, s->streams[mp3->audio_stream_idx]->nb_frames);
-        avio_seek(s->pb, 0, SEEK_END);
-    }
-
-    avio_flush(s->pb);
+    if (mp3->xing_offset)
+        mp3_update_xing(s);
 
     return 0;
 }
@@ -209,7 +310,6 @@ AVOutputFormat ff_mp2_muxer = {
     .audio_codec       = AV_CODEC_ID_MP2,
     .video_codec       = AV_CODEC_ID_NONE,
     .write_packet      = ff_raw_write_packet,
-    .write_trailer     = mp3_write_trailer,
     .flags             = AVFMT_NOTIMESTAMPS,
 };
 #endif
@@ -251,7 +351,7 @@ static int mp3_write_packet(AVFormatContext *s, AVPacket *pkt)
                 mp3->queue = pktl;
             mp3->queue_end = pktl;
         } else
-            return ff_raw_write_packet(s, pkt);
+            return mp3_write_audio_packet(s, pkt);
     } else {
         int ret;