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Deal with incomplete PMT streams in BBC iPlayer IPTV

Fixes #9926

It turns out that the test recording (and presumably the others from the same
source) contain incomplete PMT tables.  The size field for the PMT says that
there will be 383 bytes of data, but the only data received is the 182 bytes
contained in the rest of that TS packet. i

FFmpeg without MythTV modifications to mpegts.c can handle this just fine as
it doesn't need to know about the contents of the PMT.  MythTV, however,
depends on that information to determine what video and audio streams we have.

To deal with this without affecting "normal" recordings, I have put in another
fallback that will try to parse the PMT overriding the length to the length
received in the TS packet.  This will only be used if it can not be parsed
correctly, and if we've tried again without checking the CRC.  This third and
final attempt, should it fail, will cause it to give up.  Should it succeed,
there may be some streams not parsed, but whatever was in the first 182 bytes
of the PMT should be taken into consideration, and there should be playback.
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Beirdo committed Jul 25, 2011
1 parent fbf80c2 commit c11ee69c81198dc221c874e8132f1f30a385fa63
Showing with 51 additions and 15 deletions.
  1. +51 −15 mythtv/external/FFmpeg/libavformat/mpegts.c
@@ -90,6 +90,12 @@ struct MpegTSFilter {
int pid;
int last_cc; /* last cc code (-1 if first packet) */
enum MpegTSFilterType type;
/** if set, chop off PMT at the end of the TS packet, regardless of the
* data length given in the packet. This is for use by BBC iPlayer IPTV
* recordings which seem to only want to send the first packet of the PMT
* but give a length that requires 3 packets. Without this, those
* recordings are unplayable */
int pmt_chop_at_ts;
union {
MpegTSPESFilter pes_filter;
MpegTSSectionFilter section_filter;
@@ -330,16 +336,30 @@ static void write_section_data(AVFormatContext *s, MpegTSFilter *tss1,
sect->new_packet = 1;
}
while (!tss->end_of_section_reached) {
/* compute section length if possible */
if (tss->section_h_size == -1 && tss->section_index >= 3) {
len = (AV_RB16(tss->section_buf + 1) & 0xfff) + 3;
if (len > 4096)
return;
tss->section_h_size = len;
}
/* compute section length if possible */
if (tss->section_h_size == -1 && tss->section_index >= 3) {
len = (AV_RB16(tss->section_buf + 1) & 0xfff) + 3;
if (len > 4096)
return;
tss->section_h_size = len;
}

if (tss->section_h_size == -1 || tss->section_index < tss->section_h_size)
break;
if (tss->section_h_size == -1 ||
tss->section_index < tss->section_h_size)
{
if (tss1->pmt_chop_at_ts && tss->section_buf[0] == PMT_TID)
{
/* HACK! To allow BBC IPTV streams with incomplete PMTs (they
* advertise a length of 383, but only send 182 bytes!), we
* will not wait for the remainder of the PMT, but accept just
* what is in the first TS payload, as this is enough to get
* playback, although some PIDs may be filtered out as a result
*/
tss->section_h_size = tss->section_index;
}
else
break;
}

if (!tss->check_crc ||
av_crc(av_crc_get_table(AV_CRC_32_IEEE), -1,
@@ -348,7 +368,8 @@ static void write_section_data(AVFormatContext *s, MpegTSFilter *tss1,

if (tss->section_index > tss->section_h_size) {
int left = tss->section_index - tss->section_h_size;
memmove(tss->section_buf, tss->section_buf+tss->section_h_size, left);
memmove(tss->section_buf, tss->section_buf+tss->section_h_size,
left);
tss->section_index = left;
tss->section_h_size = -1;
} else {
@@ -383,6 +404,7 @@ static MpegTSFilter *mpegts_open_section_filter(MpegTSContext *ts, unsigned int
filter->type = MPEGTS_SECTION;
filter->pid = pid;
filter->last_cc = -1;
filter->pmt_chop_at_ts = 0;
sec = &filter->u.section_filter;
sec->section_cb = section_cb;
sec->opaque = opaque;
@@ -2292,7 +2314,8 @@ static int mpegts_read_header(AVFormatContext *s,
goto fail;
}
ts->raw_packet_size = get_packet_size(buf, sizeof(buf));
av_log(NULL, AV_LOG_DEBUG, "mpegts_read_header: TS packet size = %d\n", ts->raw_packet_size);
av_log(NULL, AV_LOG_DEBUG, "mpegts_read_header: TS packet size = %d\n",
ts->raw_packet_size);
if (ts->raw_packet_size <= 0)
{
av_log(NULL, AV_LOG_ERROR, "mpegts_read_header: "
@@ -2331,14 +2354,13 @@ static int mpegts_read_header(AVFormatContext *s,
s->ctx_flags |= AVFMTCTX_NOHEADER;
goto do_pcr;
}

ts->scanning = 1;
ts->pmt_scan_state = PMT_NOT_YET_FOUND;
/* tune to first service found */
for (i = 0; ((i < ts->nb_prg) &&
(ts->pmt_scan_state == PMT_NOT_YET_FOUND)); i++)
{

#ifdef DEBUG
av_log(ts->stream, AV_LOG_DEBUG, "Tuning to pnum: 0x%x\n",
ts->prg[i].id);
@@ -2357,8 +2379,7 @@ static int mpegts_read_header(AVFormatContext *s,
(ts->pmt_scan_state == PMT_NOT_YET_FOUND))
{
av_log(NULL, AV_LOG_ERROR,
"Tuning to pnum: 0x%x "
"without CRC check on PMT\n",
"Tuning to pnum: 0x%x without CRC check on PMT\n",
ts->prg[i].id);
/* turn off crc checking */
ts->pmt_filter->u.section_filter.check_crc = 0;
@@ -2367,6 +2388,21 @@ static int mpegts_read_header(AVFormatContext *s,
ts->req_sid = sid = ts->prg[i].id;
handle_packets(ts, s->probesize / ts->raw_packet_size);
}

/* fallback code to deal with streams that are not complete PMT
* streams (BBC iPlayer IPTV as an example) */
if (ts->pmt_filter &&
(ts->pmt_scan_state == PMT_NOT_YET_FOUND))
{
av_log(NULL, AV_LOG_ERROR,
"Overriding PMT data length, using "
"contents of first TS packet only!\n");
ts->pmt_filter->pmt_chop_at_ts = 1;
/* try again */
url_fseek(pb, pos, SEEK_SET);
ts->req_sid = sid = ts->prg[i].id;
handle_packets(ts, s->probesize / ts->raw_packet_size);
}
}
ts->scanning = 0;

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