Missing Teletext Subtitles in Recordings

[angela.schmid@…]

I notice a lot of missing CC text from Teletext Subtitles in DVB-C recordings independent of the recorded channel.

VLC, ccextractor, FFmpeg 3.2.4 show all CC text correct. MythTV player and mythccextractor miss almost every second/third CC text. In a recording Myth found only 732 of 1651 total.

Inspecting the ccextractor generated srt file doesn’t show any timing problems, which could be misinterpreted by MythTV.

I tried VBI debugging, but no CC text was logged.

Also no “subtl timecode” from libs/libmythtv/avformatdecoder.cpp AvFormatDecoder::ProcessSubtitlePacket? although proper debugging options were set.

Appreciate any pointers where to add some debugging to help.

[Karl.Landmann@…]

Having the same problem as described above.

Please find at the following link a 1min, 75mb recording showing the subtitle problem: ​https://file.town/download/e3ka02xyqoncxn279att8llya

subtitle extraction with mythccextractor, having a lot of missing subtitles. The second shown subtitle for example lasts for 16 seconds, missing 6 other subtitles. ​https://file.town/uploaded/itqaxntn5ymjm3yh7kqxovsl3

subtitle extraction with ccextractor showing all subtitles correct: ​https://file.town/uploaded/lxf1t0427pn8mgrm16yxymri5

I am hearing impaired, hoping you could have a look into this issue.

[angela.schmid@…]

The above patch fixes the missing teletext subtitle problem, it implements "Teletext Magazin Serial Mode".

Only Parallel Mode was implemented, therefor some subtitles where not displayed when there where not enough teletext page changes in the magazin where the subtitle pages where gathered. In Magazin Serial Mode any new page finishes the previously gathered teletext pages independently of the magazin of the new page.

[Karl.Landmann@…]

Hi Angela, on all channels I have perfect subtitles now. Great job, thanks for the fix. Karl

[weworama@…]

Hi, I am assuming that as this bug report has not been closed, you are still working on it. Also that the code also applies to CEA 608/708 subtitles / closed captions on DVB-T recordings. If either is not the case, I can submit another bug specific to DVB-T.

Our family has noted, in DVB-T recordings, all the same behavior discussed in the original thread, although we have not recently noticed the problem fixed in your patch.

In addition, some recordings captions are garbled/strange/poorly decoded(?). I have posted a ~1 minute/ ~150Mb sample file ​http://www.gigasize.com/get/two5x6jrn7b that shows myth seems to have difficulty with 708 captions on recordings. The two srt files (mythccextractor) ​http://www.gigasize.com/get/mbft418ywmc 608 srtfile ​http://www.gigasize.com/get/n005g7b2c0c 708 srt file.

This problem seems to cascade/include other behaviour, which might be related, but I do not yet have a good sample for any of those.

Wayne

Current mythtv version info - although this was recorded with a slightly earlier version of myth.

MythTV Version : v0.28.1-38-geef6a48 MythTV Branch : fixes/0.28 Network Protocol : 88 Library API : 0.28.20161120-1 QT Version : 5.5.1 Options compiled in: linux profile use_hidesyms using_alsa using_oss using_pulse using_pulseoutput using_backend using_bindings_perl using_bindings_python using_bindings_php using_crystalhd using_dvb using_firewire using_frontend using_hdhomerun using_vbox using_ceton using_hdpvr using_ivtv using_joystick_menu using_libcec using_libcrypto using_libdns_sd using_libfftw3 using_libxml2 using_lirc using_mheg using_opengl using_opengl_video using_opengl_themepainter using_qtwebkit using_qtscript using_qtdbus using_sdl using_taglib using_v4l2 using_x11 using_xra ndr using_xv using_profiletype using_bindings_perl using_bindings_python using_bindings_php using_freetype2 using_mythtranscode using_opengl using_vaapi using_vdpau using_ffmpeg_threads using_mheg using_libass using_libxml2

Vlc displays the CEA 608 captions in the original 18+ Gb file, but apparently didn’t recognize the presence of the second channel. The posted portion was cut with avidemux, using the mpg ts demuxer as that seems to be keeping the extra streams intact.

[angela.schmid@…]

@weworama

The patch fixes the original problem about missing subtitles. It was fixed by implementing "Teletext Magazin Serial Mode". The original issue is solved and I hope to see it integrated in the next Mythtv release.

Please create a new issue for your garbled captions.

[Peter Bennett]

I would like to validate the patch. There are no teletext subtitles where I live, so I downloaded some files with teletext magazine subtitles. I do not see any missing subtitle when I play it on current master. Can you supply a test file or tell me what to do to see the problem.

TS Reader Lite shows this on two files I downloaded and the subtitles seem to be fine on existing MythTV master:

Elementary Stream PID 258 (0x0102) Teletext/VBI
Descriptor: Teletext Descriptor
 Language: und Type: Initial Teletext page Magazine: 0x01 Page: 0x00
 Language: swe Type: Teletext subtitle page Magazine: 0x01 Page: 0x99
 Language: nor Type: Teletext subtitle page Magazine: 0x02 Page: 0x99
 Language: dan Type: Teletext subtitle page Magazine: 0x05 Page: 0x99
 Language: fin Type: Teletext subtitle page Magazine: 0x06 Page: 0x99
 Language: swe Type: Initial Teletext page Magazine: 0x01 Page: 0x01
 Language: nor Type: Initial Teletext page Magazine: 0x02 Page: 0x01
 Language: dan Type: Initial Teletext page Magazine: 0x05 Page: 0x01
 Language: fin Type: Initial Teletext page Magazine: 0x06 Page: 0x01

Elementary Stream PID 5303 (0x14b7) Teletext/VBI
Descriptor: Stream Identifier Descriptor
 04                                               .               
Descriptor: Teletext Descriptor
 Language: eng Type: Teletext subtitle page Magazine: 0x00 Page: 0x88
 Language: eng Type: Initial Teletext page Magazine: 0x00 Page: 0x88
Descriptor: Private Data Indicator Descriptor
 4f 54 56 00                                      OTV.            
Descriptor: User Private Descriptor: 0xfe
 53 55 42 00                                      SUB.            

[Jonatan Lindblad]

Minor formatting to adhere more closely to the coding standards available at ​https://www.mythtv.org/wiki/Coding_Standards

[Jonatan Lindblad]

Thank you for the patch. I tried it and it also fixes #12877 which has a link to a sample.

[Peter Bennett]

I tested using the sample file from #12877. This patch fixes that and does not affect subtitles in other test files I was using.

[Angela Schmidt <angela.schmid@…>]

In 39c9292fdc9385dbee25faf5bca8ca6b1d67b31b/mythtv:

Fix the missing teletext subtitle problem

Implements "Teletext Magazin Serial Mode".

Only Parallel Mode was implemented, therefor some subtitles where not
displayed when there where not enough teletext page changes in the
magazin where the subtitle pages where gathered. In Magazin Serial
Mode any new page finishes the previously gathered teletext pages
independently of the magazin of the new page.

Fixes #13016

Signed-off-by: Peter Bennett <pbennett@…>

[Angela Schmidt <angela.schmid@…>]

In 5dce69fbb52c03739f9ca379fbb8e7885b45bd95/mythtv:

Fix the missing teletext subtitle problem

Implements "Teletext Magazin Serial Mode".

Only Parallel Mode was implemented, therefor some subtitles where not
displayed when there where not enough teletext page changes in the
magazin where the subtitle pages where gathered. In Magazin Serial
Mode any new page finishes the previously gathered teletext pages
independently of the magazin of the new page.

Fixes #13016

Signed-off-by: Peter Bennett <pbennett@…>
(cherry picked from commit 39c9292fdc9385dbee25faf5bca8ca6b1d67b31b)