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• How the ffmpeg is fixing Handle page termination with same page number ...? [closed]

  11 avril 2024, par adarsh

  Im working on the teletext subtitle feature and faced with subs not clearing issue.
the subtitle lines remain displayed until being replaced by a new version of the specific line. So the subtitles never disappear and often an old line is still displayed, after another, more recent line is displayed/updated.
take a look at the issue in this sample video file : https://code.videolan.org/videolan/vlc/uploads/58c2e1660e94e2df5e8cdb75edf531d9/GODFATHER__03_.ts
Issue reported : https://sourceforge.net/p/zapping/bugs/203/

  


  The player is using ffmpeg and libzvbi library.

  


  At first I suspected that the Erase Page Flag (C4) in the Page Header was not set, but the flag was indeed set (at least once between two LOPs with subtitles). After further debugging it turned out that the Teletext service in the two issues consists of just a single Teletext page - which is the reason here :

  


  The Teletext spec defines the Magazine Serial Flag (C11) in Table 2 (ETSI EN 300 706 v1.2.1) as (bold font by me) :

  


  When set to '1' the service is designated to be in Serial mode and the transmission of a page is terminated by the next page header with a different page number.
When set to '0' the service is designated to be in Parallel mode and the transmission of a page is terminated by the next page header with a different page number but the same magazine number.
The same setting shall be used for all page headers in the service.
(BTW it doesn't really matter, but in these two cases this flag is always 0)

  


  In vbi_decode_teletext in /src/packet.c, storing the page is aborted, if the condition "page terminated" in the C11 definition is not met. But as the service here consists of only one page, this condition is never met !

  


  Luckily, this issue was fixed in ffmpeg- https://github.com/FFmpeg/FFmpeg/commit/b1e0e216462a989a39e7b413aef6d32f8cedc154

  


  and also in zvbi :
https://github.com/zapping-vbi/zvbi/commit/40a6ab0200c46b67b059b5b1fb15793ce780892a

  


  I understand the root cause and fix in zvbi library, and how it is ignoring c4 flag in case the same page no.

  


  But i want to understand how the ffmpeg fix is working ?
ffmpeg fix : https://github.com/FFmpeg/FFmpeg/commit/b1e0e216462a989a39e7b413aef6d32f8cedc154

  


  what is the rule for repeated page headers ?

  


• Revision 29932 : Premier commit qui casse un peu la compat avec l’ancienne version ... On ...

  17 juillet 2009, par kent1@… — Log

  Premier commit qui casse un peu la compat avec l’ancienne version ...
  On passe la configuration en #FORMULAIRE_CONFIG_
  On prépare la possibilité d’avoir des statistiques du privé et d’enlever des statistiques certains statuts

• avcodec/mediacodecdec : fix SEGV on modern nvidia decoders

  31 juillet 2018, par Aman Gupta

  avcodec/mediacodecdec : fix SEGV on modern nvidia decoders
  This code came originally from gstreamer, where it was added in [1]
  
  as a work-around for the Tegra 3. (The alignment was changed in [2]
  
  as a response to [3], from 32-bit to 16-bit).
  gstreamer only used this workaround in the case where the decoder
  
  didn't return a slice-height property, but when the code was copied
  
  into avcodec the conditional got lost. This commit restores the guard
  
  and prefers the slice-height from the decoder when it is available.
  This fixes segfaults decoding 1920x1080 h264 and mpeg2 videos on the
  
  NVidia SHIELD after upgrading to Android Oreo.
  [1] https://github.com/GStreamer/gst-plugins-bad/commit/a870e6a5c30dd85240fe75c7409cc1cf1b86541d
  
  [2] https://github.com/GStreamer/gst-plugins-bad/commit/21ff3ae0b0127bd82951d278ca24f2d54133b7cd
  
  [3] https://bugzilla.gnome.org/show_bug.cgi?id=748867
  Signed-off-by : Aman Gupta <aman@tmm1.net>
  

  • [DH] libavcodec/mediacodecdec_common.c