avformat/mpegts: parse sections with multiple tables
authorAman Gupta <aman@tmm1.net>
Wed, 9 May 2018 21:20:48 +0000 (14:20 -0700)
committerAman Gupta <aman@tmm1.net>
Sat, 12 May 2018 18:50:00 +0000 (11:50 -0700)
Fixes PMT parsing in some mpegts streams which contain
multiple tables within the PMT pid. Previously, the parser
assumed only one table was present in each packet, and discarded
the rest of the section data after attempting to parse the first
table.

A similar issue was documented in the BeyondTV software[1], which
helped me diagnose the same bug in the ffmpeg mpegts demuxer. I also
tried DVBInspector, libdvbpsi's dvbinfo, and tstools' tsinfo to
help debug. The former two properly read PMTs with multiple tables,
whereas the last has the same bug as ffmpeg.

I've created a minimal sample[2] which contains the combined PMT.
Here's what ffmpeg probe shows before and after this patch:

Before:

    Input #0, mpegts, from 'combined-pmt-tids.ts':
      Duration: 00:00:01.08, start: 4932.966167, bitrate: 741 kb/s
      Program 1
      No Program
        Stream #0:0[0xf9d]: Audio: ac3, 48000 Hz, mono, fltp, 96 kb/s
        Stream #0:1[0xf9b]: Audio: mp3, 0 channels, fltp
        Stream #0:2[0xf9c]: Unknown: none

After:

    Input #0, mpegts, from 'combined-pmt-tids.ts':
      Duration: 00:00:01.11, start: 4932.966167, bitrate: 718 kb/s
      Program 1
        Stream #0:0[0xf9b]: Video: mpeg2video ([2][0][0][0] / 0x0002), none(tv, top first), 29.97 fps, 29.97 tbr, 90k tbn, 90k tbc
        Stream #0:1[0xf9c](eng): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, 5.1(side), fltp, 384 kb/s
        Stream #0:2[0xf9d](spa): Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, mono, fltp, 96 kb/s

With the patch, the PMT is parsed correctly so the streams are
created in the correct order, are associated with "Program 1",
and their codecs are set correctly.

[1] http://forums.snapstream.com/vb/showpost.php?p=343816&postcount=201
[2] https://s3.amazonaws.com/tmm1/combined-pmt-tids.ts

Signed-off-by: Aman Gupta <aman@tmm1.net>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
libavformat/mpegts.c

index 0d1dda1..3c9f942 100644 (file)
@@ -391,7 +391,8 @@ static void write_section_data(MpegTSContext *ts, MpegTSFilter *tss1,
                                const uint8_t *buf, int buf_size, int is_start)
 {
     MpegTSSectionFilter *tss = &tss1->u.section_filter;
-    int len;
+    uint8_t *cur_section_buf = NULL;
+    int len, offset;
 
     if (is_start) {
         memcpy(tss->section_buf, buf, buf_size);
@@ -408,23 +409,26 @@ static void write_section_data(MpegTSContext *ts, MpegTSFilter *tss1,
         tss->section_index += len;
     }
 
+    offset = 0;
+    cur_section_buf = tss->section_buf;
+    while (cur_section_buf - tss->section_buf < MAX_SECTION_SIZE && cur_section_buf[0] != 0xff) {
     /* 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 (tss->section_h_size == -1 && tss->section_index - offset >= 3) {
+        len = (AV_RB16(cur_section_buf + 1) & 0xfff) + 3;
         if (len > MAX_SECTION_SIZE)
             return;
         tss->section_h_size = len;
     }
 
     if (tss->section_h_size != -1 &&
-        tss->section_index >= tss->section_h_size) {
+        tss->section_index >= offset + tss->section_h_size) {
         int crc_valid = 1;
         tss->end_of_section_reached = 1;
 
         if (tss->check_crc) {
-            crc_valid = !av_crc(av_crc_get_table(AV_CRC_32_IEEE), -1, tss->section_buf, tss->section_h_size);
+            crc_valid = !av_crc(av_crc_get_table(AV_CRC_32_IEEE), -1, cur_section_buf, tss->section_h_size);
             if (tss->section_h_size >= 4)
-                tss->crc = AV_RB32(tss->section_buf + tss->section_h_size - 4);
+                tss->crc = AV_RB32(cur_section_buf + tss->section_h_size - 4);
 
             if (crc_valid) {
                 ts->crc_validity[ tss1->pid ] = 100;
@@ -434,10 +438,18 @@ static void write_section_data(MpegTSContext *ts, MpegTSFilter *tss1,
                 crc_valid = 2;
         }
         if (crc_valid) {
-            tss->section_cb(tss1, tss->section_buf, tss->section_h_size);
+            tss->section_cb(tss1, cur_section_buf, tss->section_h_size);
             if (crc_valid != 1)
                 tss->last_ver = -1;
         }
+
+        cur_section_buf += tss->section_h_size;
+        offset += tss->section_h_size;
+        tss->section_h_size = -1;
+    } else {
+        tss->end_of_section_reached = 0;
+        break;
+    }
     }
 }