lavf/mp3enc: write encoder delay/padding upon closing

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavformat/mp3enc.c

@@ -111,6 +111,8 @@ typedef struct MP3Context {
     uint64_t bag[XING_NUM_BAGS];
     int initial_bitrate;
     int has_variable_bitrate;
+    int delay;
+    int padding;
 
     /* index of the audio stream */
     int audio_stream_idx;
@@ -247,12 +249,7 @@ static int mp3_write_xing(AVFormatContext *s)
     ffio_fill(dyn_ctx, 0, 8); // empty replaygain fields
     avio_w8(dyn_ctx, 0);      // unknown encoding flags
     avio_w8(dyn_ctx, 0);      // unknown abr/minimal bitrate
-
-    // encoder delay
-    if (par->initial_padding - 528 - 1 >= 1 << 12) {
-        av_log(s, AV_LOG_WARNING, "Too many samples of initial padding.\n");
-    }
-    avio_wb24(dyn_ctx, FFMAX(par->initial_padding - 528 - 1, 0)<<12);
+    avio_wb24(dyn_ctx, 0);    // empty encoder delay/padding
 
     avio_w8(dyn_ctx,   0); // misc
     avio_w8(dyn_ctx,   0); // mp3gain
@@ -345,10 +342,24 @@ static int mp3_write_audio_packet(AVFormatContext *s, AVPacket *pkt)
 #endif
 
         if (mp3->xing_offset) {
+            uint8_t *side_data = NULL;
+            int side_data_size = 0;
+
             mp3_xing_add_frame(mp3, pkt);
             mp3->audio_size += pkt->size;
             mp3->audio_crc   = av_crc(av_crc_get_table(AV_CRC_16_ANSI_LE),
                                       mp3->audio_crc, pkt->data, pkt->size);
+
+            side_data = av_packet_get_side_data(pkt,
+                                                AV_PKT_DATA_SKIP_SAMPLES,
+                                                &side_data_size);
+            if (side_data && side_data_size >= 10) {
+                mp3->padding = FFMAX(AV_RL32(side_data + 4) + 528 + 1, 0);
+                if (!mp3->delay)
+                    mp3->delay =  FFMAX(AV_RL32(side_data) - 528 - 1, 0);
+            } else {
+                mp3->padding = 0;
+            }
         }
     }
 
@@ -422,6 +433,17 @@ static void mp3_update_xing(AVFormatContext *s)
         }
     }
 
+    /* write encoder delay/padding */
+    if (mp3->delay >= 1 << 12) {
+        mp3->delay = (1 << 12) - 1;
+        av_log(s, AV_LOG_WARNING, "Too many samples of initial padding.\n");
+    }
+    if (mp3->padding >= 1 << 12) {
+        mp3->padding = (1 << 12) - 1;
+        av_log(s, AV_LOG_WARNING, "Too many samples of trailing padding.\n");
+    }
+    AV_WB24(mp3->xing_frame + mp3->xing_offset + 141, (mp3->delay << 12) + mp3->padding);
+
     AV_WB32(mp3->xing_frame + mp3->xing_offset + XING_SIZE - 8, mp3->audio_size);
     AV_WB16(mp3->xing_frame + mp3->xing_offset + XING_SIZE - 4, mp3->audio_crc);