dvbsub: fix encoding of termination packets.

The old code generates a termination packet with the same regions as the
start packet and page_state set to "only what changed"; the result is
that the termination packet is decoded as identical to the start packet.

The new code does as found in some DVB broadcasts: produce a packet with
no regions. This is done by expecting num_rects to be 0 rather than
using a flip-flop. ffmpeg.c is updated accordingly.

ffmpeg.c

@@ -703,6 +703,8 @@ static void do_subtitle_out(AVFormatContext *s,
         sub->pts               += av_rescale_q(sub->start_display_time, (AVRational){ 1, 1000 }, AV_TIME_BASE_Q);
         sub->end_display_time  -= sub->start_display_time;
         sub->start_display_time = 0;
+        if (i == 1)
+            sub->num_rects = 0;
         subtitle_out_size = avcodec_encode_subtitle(enc, subtitle_out,
                                                     subtitle_out_max_size, sub);
         if (subtitle_out_size < 0) {

libavcodec/dvbsub.c

@@ -23,7 +23,6 @@
 #include "libavutil/colorspace.h"
 
 typedef struct DVBSubtitleContext {
-    int hide_state;
     int object_version;
 } DVBSubtitleContext;
 
@@ -259,7 +258,7 @@ static int encode_dvb_subtitles(DVBSubtitleContext *s,
 
     page_id = 1;
 
-    if (h->num_rects == 0 || h->rects == NULL)
+    if (h->num_rects && h->rects == NULL)
         return -1;
 
     *q++ = 0x00; /* subtitle_stream_id */
@@ -272,9 +271,6 @@ static int encode_dvb_subtitles(DVBSubtitleContext *s,
     pseg_len = q;
     q += 2; /* segment length */
     *q++ = 30; /* page_timeout (seconds) */
-    if (s->hide_state)
-        page_state = 0; /* normal case */
-    else
     page_state = 2; /* mode change */
     /* page_version = 0 + page_state */
     *q++ = (s->object_version << 4) | (page_state << 2) | 3;
@@ -288,7 +284,7 @@ static int encode_dvb_subtitles(DVBSubtitleContext *s,
 
     bytestream_put_be16(&pseg_len, q - pseg_len - 2);
 
-    if (!s->hide_state) {
+    if (h->num_rects) {
         for (clut_id = 0; clut_id < h->num_rects; clut_id++) {
 
             /* CLUT segment */
@@ -366,18 +362,17 @@ static int encode_dvb_subtitles(DVBSubtitleContext *s,
         *q++ = 0; /* 8 bit fill colors */
         *q++ = 0x03; /* 4 bit and 2 bit fill colors */
 
-        if (!s->hide_state) {
+        /* TODO reindent */
             bytestream_put_be16(&q, region_id); /* object_id == region_id */
             *q++ = (0 << 6) | (0 << 4);
             *q++ = 0;
             *q++ = 0xf0;
             *q++ = 0;
-        }
 
         bytestream_put_be16(&pseg_len, q - pseg_len - 2);
     }
 
-    if (!s->hide_state) {
+    if (h->num_rects) {
 
         for (object_id = 0; object_id < h->num_rects; object_id++) {
             void (*dvb_encode_rle)(uint8_t **pq,
@@ -446,7 +441,6 @@ static int encode_dvb_subtitles(DVBSubtitleContext *s,
     *q++ = 0xff; /* end of PES data */
 
     s->object_version = (s->object_version + 1) & 0xf;
-    s->hide_state = !s->hide_state;
     return q - outbuf;
 }