assert failure in CC708Decoder::decode_cc_data / parse_cc_packet

[Robert Tsai <rtsai1111>]

I have a slightly damaged OTA HD recording that triggers this assert when running mythcommflag against it; it looks like the data contains something unexpected:

(gdb) bt           
#0  0x00002aaaae6480fd in raise () from /lib/libc.so.6
#1  0x00002aaaae64982e in abort () from /lib/libc.so.6
#2  0x00002aaaae6418d1 in __assert_fail () from /lib/libc.so.6
#3  0x00002aaaab20d212 in parse_cc_packet (cb_cbs=0x69fd38, pkt=0x6e9fe0)
    at cc708decoder.cpp:584
#4  0x00002aaaab20d35d in CC708Decoder::decode_cc_data (this=0x6e9fe0, 
    cc_type=3, data1=195, data2=34) at cc708decoder.cpp:67
#5  0x00002aaaab3044e5 in decode_cc_atsc (s=0x706ff0, buf=0x2aaab5a5f02b "J", 
    sz=9379) at avformatdecoder.cpp:1548
#6  0x00002aaaabddb1b2 in mpeg_decode_user_data (avctx=0xffffffffffffffff, 
    buf=0x69d8 <Address 0x69d8 out of bounds>, buf_size=6) at mpeg12.c:2977
#7  0x00002aaaabddb66f in mpeg_decode_frame (avctx=0x706ff0, data=Variable "data" is not available.
)
    at mpeg12.c:3150
#8  0x00002aaaabd256d7 in avcodec_decode_video (avctx=0x706ff0, 
    picture=0x7fffff835c60, got_picture_ptr=0x7fffff835e1c, 
    buf=0x2aaab5a5f010 "", buf_size=9406) at utils.c:948
#9  0x00002aaaab31330b in AvFormatDecoder::GetFrame (this=0x6e8f80, 
    onlyvideo=1) at avformatdecoder.cpp:2627
#10 0x00002aaaab2d4620 in NuppelVideoPlayer::GetFrameNormal (this=0x69fd30, 
    onlyvideo=1) at NuppelVideoPlayer.cpp:1020
#11 0x00002aaaab2d5278 in NuppelVideoPlayer::GetFrame (this=0x69fd30, 
    onlyvideo=1, unsafe=true) at NuppelVideoPlayer.cpp:1098
#12 0x00002aaaab2e5d37 in NuppelVideoPlayer::GetRawVideoFrame (this=0x69fd30, 
    frameNumber=-1) at NuppelVideoPlayer.cpp:4442
#13 0x0000000000425d17 in ClassicCommDetector::go (this=0x6e7630)
    at ClassicCommDetector.cpp:350
#14 0x000000000040a88e in DoFlagCommercials (showPercentage=false, 
    fullSpeed=true, inJobQueue=true, nvp=0x69fd30, commDetectMethod=255)
    at main.cpp:448
#15 0x000000000040c362 in FlagCommercials (chanid=@0x7fffff837eb0, 
    starttime=@0x7fffff837ea0) at main.cpp:624
#16 0x000000000040fcc2 in main (argc=3, argv=0x7fffff838308) at main.cpp:970

(gdb) l parse_cc_packet
556         }
557     #endif
558         parse_cc_service_stream(cc, service_num);
559     }
560
561     static void parse_cc_packet(CC708Reader* cb_cbs, CaptionPacket* pkt)
562     {
563         const unsigned char* pkt_buf = pkt->data;
564         const int pkt_size = pkt->size;
565         int off = 1;
566         int service_number = 0;
567         int block_data_offset = 0;
568         int len = ((((int)pkt_buf[0])&0x3f)*2-1)&0xff;
569         int seq_num = (((int)pkt_buf[0])>>6)&0x3;
570
571     #if DEBUG_CC_RAWPACKET
572         {
573             int j;
574             fprintf(stderr, "CC length(%2i) seq_num(%i) ", len, seq_num);
575             for (j = 0; j < pkt_size; j++)
576                 fprintf(stderr, "0x%x ", pkt_buf[j]);
577             fprintf(stderr, "\n");
578         }
579     #else
580         (void) seq_num;
581     #endif
582
583         assert(pkt_size<127);
584         assert(len<128);
585

(gdb) p /x len
$17 = 0xff
(gdb) p /x pkt_buf[0]
$18 = 0x80
(gdb) p (((int)pkt_buf[0])&0x3f)*2-1
$19 = -1

I can't help debug this, but I can help test a patch, since I have a recording that seems to always trigger this assert failure. FWIW, this is last night's broadcast of Fox 24.

[danielk]

(In [9210]) Fixes #1423. Fixes segfault by printing out debug info rather than crashing.

[danielk]

duplicate of #1408.