[Bug 758651] Fail to play MPEG2 video clip in file container format MPEG-PS in manual gst command pipeline

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=758651

--- Comment #10 from Austin Yuan <shengquan.yuan at intel.com> ---
Bellow is MPEG2PS spec and MPEG1PS spec for the pack_header syntax:

ISO13818-1:
pack_header() { 
    pack_start_code              32  bslbf 
    '01'                      2 bslbf 
    system_clock_reference_base [32..30]      3  bslbf 
    marker_bit                  1  bslbf 
    ........
}

ISO11172-1
pack() {
    pack_start_code                32 bslbf
    '0010'                    4 bslbf
    system_clock_reference [32..30]        3 bslbf
    marker_bit                1 bslbf
    ...........
}

mpegdemux gstmpegdemux.c:gst_ps_demux_parse_pack_start follows above spec:

static GstFlowReturn
gst_ps_demux_parse_pack_start (GstPsDemux * demux)
{
    ...........

  /* skip start code */
  data += 4;
  ...........

  /* start parsing the stream */
  if ((*data & 0xc0) == 0x40) {
    guint32 scr_ext;
    guint32 next32;
    guint8 stuffing_bytes;

    GST_LOG ("Found MPEG2 stream");
    demux->is_mpeg2_pack = TRUE;
    ...........
  } else {
    GST_DEBUG ("Found MPEG1 stream");
    demux->is_mpeg2_pack = FALSE;

    /* check markers */
    if (G_UNLIKELY ((scr1 & 0xf1000100) != 0x21000100))
      goto lost_sync;
    ...........
  }
  ...........
}

Check the clip, it will fall into gstmpegdemux.c:gst_ps_demux_parse_pack_start
MPEG1 code path according to ISO13818-1/ISO11172-1: 

hexdump -C Gonegirl_640x320_6mbps_30fps_Main at High.mpg
00000000  00 00 01 ba 21 00 01 00  01 80 7b 3f 00 00 01 bb  |....!.....{?....|
00000010  00 09 80 7b 3f 00 21 ff  e0 e0 e6 00 00 01 e0 07  |...{?.!.........|
00000020  df 31 00 03 77 01 11 00  03 5f 91 00 00 01 b3 28  |.1..w...._.....(|
00000030  01 40 15 0e a6 23 80 00  00 01 b5 14 4a 00 01 00  |. at ...#......J...|
00000040  00 00 00 01 b8 00 08 00  40 00 00 01 00 00 0a 84  |........ at .......|

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