wg <[email protected]> added the comment:
Just now noticed this issue. I hit the same problem last year and fixed it;
here is what I wrote to Ian Caulfield to explain the patch:
--------------------------------------------------
Analysis has shown that in this case the
if (s->last_pts != s->pts && s->pts != AV_NOPTS_VALUE) /* Start of a new
packet */
check gets "stuck" and is never true (even though more correct dvbsub
packets keep arriving). I then looked at other parsers and _none_ of
them use the pts values for detecting packet start; the last_pts and
fetch_timestamp fields are even marked "private" in the parser header
file, so I suppose they shouldn't really be used at all in the parser.
So I rewrote that part of the parser detecting the start code and then
parsing segments as before, but without any pts touching. Now
everything works fine with all samples that I have. The parser is now
also slightly smaller and more efficient, as it doesn't keep
re-examining the complete packet for segments.
Please take a look -- the diff is long; but it's probably better to
look at it as a rewrite.
____________________________________________________
FFmpeg issue tracker <[email protected]>
<https://roundup.ffmpeg.org/roundup/ffmpeg/issue536>
____________________________________________________--- trunk/libavcodec/dvbsub_parser.c 2008-06-02 21:18:47.000000000 +0200
+++ ffmpeg-wg/libavcodec/dvbsub_parser.c 2008-12-24 17:10:58.000000000 +0100
@@ -33,7 +33,7 @@
/* parser definition */
typedef struct DVBSubParseContext {
uint8_t *packet_buf;
- int packet_start;
+ int cursor;
int packet_index;
int in_packet;
} DVBSubParseContext;
@@ -52,8 +52,6 @@
const uint8_t *buf, int buf_size)
{
DVBSubParseContext *pc = s->priv_data;
- uint8_t *p, *p_end;
- int len, buf_pos = 0;
#ifdef DEBUG
av_log(avctx, AV_LOG_INFO, "DVB parse packet pts=%"PRIx64", lpts=%"PRIx64", cpts=%"PRIx64":\n",
@@ -78,106 +76,60 @@
*poutbuf = NULL;
*poutbuf_size = 0;
- s->fetch_timestamp = 1;
-
- if (s->last_pts != s->pts && s->pts != AV_NOPTS_VALUE) /* Start of a new packet */
- {
- if (pc->packet_index != pc->packet_start)
- {
-#ifdef DEBUG
- av_log(avctx, AV_LOG_INFO, "Discarding %d bytes\n",
- pc->packet_index - pc->packet_start);
-#endif
- }
-
- pc->packet_start = 0;
- pc->packet_index = 0;
-
+ if (!pc->in_packet) {
if (buf_size < 2 || buf[0] != 0x20 || buf[1] != 0x00) {
#ifdef DEBUG
av_log(avctx, AV_LOG_INFO, "Bad packet header\n");
#endif
- return -1;
+ return buf_size; /* discard data */
}
-
- buf_pos = 2;
-
+ if (buf_size-2 > PARSE_BUF_SIZE)
+ return -1;
+ memcpy(pc->packet_buf, buf+2, buf_size-2);
+ pc->cursor = 0;
+ pc->packet_index = buf_size-2;
pc->in_packet = 1;
} else {
- if (pc->packet_start != 0)
- {
- if (pc->packet_index != pc->packet_start)
- {
- memmove(pc->packet_buf, pc->packet_buf + pc->packet_start,
- pc->packet_index - pc->packet_start);
-
- pc->packet_index -= pc->packet_start;
- pc->packet_start = 0;
- } else {
- pc->packet_start = 0;
- pc->packet_index = 0;
- }
- }
+ if (buf_size + pc->packet_index > PARSE_BUF_SIZE)
+ return -1;
+ memcpy(pc->packet_buf + pc->packet_index, buf, buf_size);
+ pc->packet_index += buf_size;
}
- if (buf_size - buf_pos + pc->packet_index > PARSE_BUF_SIZE)
- return -1;
-
-/* if not currently in a packet, discard data */
- if (pc->in_packet == 0)
- return buf_size;
-
- memcpy(pc->packet_buf + pc->packet_index, buf + buf_pos, buf_size - buf_pos);
- pc->packet_index += buf_size - buf_pos;
-
- p = pc->packet_buf;
- p_end = pc->packet_buf + pc->packet_index;
-
- while (p < p_end)
- {
- if (*p == 0x0f)
- {
- if (p + 6 <= p_end)
- {
- len = AV_RB16(p + 4);
-
- if (p + len + 6 <= p_end)
- {
- *poutbuf_size += len + 6;
+ /* parse newly obtained segments */
+ while (pc->cursor < pc->packet_index) {
+ if (pc->packet_buf[pc->cursor] == 0x0f) {
+ if (pc->cursor + 6 <= pc->packet_index) {
+ int len = AV_RB16(pc->packet_buf + pc->cursor + 4);
- p += len + 6;
+ if (pc->cursor + len + 6 <= pc->packet_index) {
+ pc->cursor += len + 6;
} else
break;
} else
break;
- } else if (*p == 0xff) {
- if (p + 1 < p_end)
- {
+ } else if (pc->packet_buf[pc->cursor] == 0xff) {
+ if (pc->cursor + 1 < pc->packet_index) {
#ifdef DEBUG
av_log(avctx, AV_LOG_INFO, "Junk at end of packet\n");
#endif
}
- pc->packet_index = p - pc->packet_buf;
+ *poutbuf = pc->packet_buf;
+ *poutbuf_size = pc->cursor;
+ pc->packet_index = 0;
pc->in_packet = 0;
+#ifdef DEBUG
+ av_log(avctx, AV_LOG_INFO, "parse packet sz:%d\n", *poutbuf_size);
+#endif
break;
} else {
av_log(avctx, AV_LOG_ERROR, "Junk in packet\n");
- pc->packet_index = p - pc->packet_buf;
pc->in_packet = 0;
break;
}
}
- if (*poutbuf_size > 0)
- {
- *poutbuf = pc->packet_buf;
- pc->packet_start = *poutbuf_size;
- }
-
- if (s->pts == AV_NOPTS_VALUE)
- s->pts = s->last_pts;
-
return buf_size;
}
