matroskadec: fix ASS subtitle track packets before emitting them

Matroska does some butchering when storing the ASS lines. The start and end
time are removed (because they are duplicated in the container).
The matroska_fix_ass_packet() function simply restore those start and end
time in ASS lines to ensure our ASS packets comply with the ASS spec.

Originally committed as revision 15211 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/matroskadec.c

@@ -28,6 +28,7 @@
  * Specs available on the Matroska project page: http://www.matroska.org/.
  */
 
+#include <stdio.h>
 #include "avformat.h"
 /* For codec_get_id(). */
 #include "riff.h"
@@ -932,6 +933,37 @@ static int matroska_decode_buffer(uint8_t** buf, int* buf_size,
     return -1;
 }
 
+static void matroska_fix_ass_packet(MatroskaDemuxContext *matroska,
+                                    AVPacket *pkt)
+{
+    char *line, *layer, *ptr = pkt->data, *end = ptr+pkt->size;
+    for (; *ptr!=',' && ptr<end-1; ptr++);
+    if (*ptr == ',')
+        layer = ++ptr;
+    for (; *ptr!=',' && ptr<end-1; ptr++);
+    if (*ptr == ',') {
+        int64_t end_pts = pkt->pts + pkt->convergence_duration;
+        int sc = matroska->time_scale * pkt->pts / 10000000;
+        int ec = matroska->time_scale * end_pts  / 10000000;
+        int sh, sm, ss, eh, em, es, len;
+        sh = sc/360000;  sc -= 360000*sh;
+        sm = sc/  6000;  sc -=   6000*sm;
+        ss = sc/   100;  sc -=    100*ss;
+        eh = ec/360000;  ec -= 360000*eh;
+        em = ec/  6000;  ec -=   6000*em;
+        es = ec/   100;  ec -=    100*es;
+        *ptr++ = '\0';
+        len = 50 + end-ptr + FF_INPUT_BUFFER_PADDING_SIZE;
+        if (!(line = av_malloc(len)))
+            return;
+        snprintf(line,len,"Dialogue: %s,%d:%02d:%02d.%02d,%d:%02d:%02d.%02d,%s",
+                 layer, sh, sm, ss, sc, eh, em, es, ec, ptr);
+        av_free(pkt->data);
+        pkt->data = line;
+        pkt->size = strlen(line);
+    }
+}
+
 static void matroska_convert_tags(AVFormatContext *s, EbmlList *list)
 {
     MatroskaTag *tags = list->elem;
@@ -1588,6 +1620,9 @@ static int matroska_parse_block(MatroskaDemuxContext *matroska, uint8_t *data,
                 else
                     pkt->duration = duration;
 
+                if (st->codec->codec_id == CODEC_ID_SSA)
+                    matroska_fix_ass_packet(matroska, pkt);
+
                 dynarray_add(&matroska->packets, &matroska->num_packets, pkt);
             }