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• Anomalie #3217 (Nouveau) : Caractères spéciaux d’expression régulière présents dans une chaîne de ...

  22 mai 2014, par Pascal Verrier

  Bonjour,

  J’ai une boucle au sein de l’affichage d’un forum qui permet d’afficher les autres posts similaires ; pour cela, l’argument recherche est renseigné avec le titre du forum en cours d’affichage.

  Cela fonctionne bien sur la plupart des pages sauf sur un forum ayant le titre suivant : Sortie du kit compatible SPIP 3 ??

  J’ai une erreur MySQL 1139 :
  

  Got error ’repetition-operator operand invalid’ from regexp
  SELECT t.id_forum, t.titre, t.texte, t.auteur, t.email_auteur, t.nom_site, t.url_site FROM spip_forum AS t WHERE t.titre REGEXP ’Sortie du kit compatible SPIP 3 ??|Sortie|compatible|SPIP’ OR ...
  

  Ce sont les ?? qui coincent car manifestament ils sont interprétés en tant que métacaractères dans la regex, n’ayant pas été échappés.

  J’ai fait un autre essai en mettant d’autres opérateurs de regex : Sortie kit[0-9]* compatib(ilité|le) SPIP 3 ??, qui confirme ce que je pensais :
  

  Erreur SQL 1139
  Got error ’repetition-operator operand invalid’ from regexp
  SELECT ... WHERE t.titre REGEXP ’Sortie kit[0-9]* compatib(ilite|le) SPIP 3 ??|Sortie|kit[0-9]*|compatib(ilite|le)|SPIP’ OR ...
  

  à savoir la chaîne de recherche n’est pas prétraitée, et les caractères spéciaux sont repris tels quels, d’où le plantage MySQL.

  Je propose donc les corrections ci-joint pour ecrire/inc/rechercher.php (commentaires avec pverrier).

• Gallery of VP8 Encoding Naivete

  15 octobre 2010, par Multimedia Mike — VP8

  I’ve been toiling away as a multimedia technology generalist for so long that it’s easy for me to forget that not everyone is as versed in the minutiae of the domain as I am. But I recently experienced what it’s like to be such an outsider when I posted about my toy VP8 encoder, expressing that it’s one of the hardest things I have ever tried to do. I heard of from number of people who do have extensive experience in video encoding, particularly with the H.264 and VP8 codecs. Their reactions were predictable : What’s so hard ? Look, you might be a little too immersed in the area to really understand a relative beginner’s perspective.

  And to all the people who suggested that I should get the encoder into FFmpeg ASAP : Are you crazy ?! Did you see what the first pass of the encoder produced ? Do you have lower standards than even I do ?

  
  
  

  Not Giving Up
  I worked a little more on the toy encoder. Remember that the above image is what I’m hoping to encode somewhat faithfully for this experiment. In my first pass, I attempted vertical prediction for all planes. For my next pass, I forced the chroma planes to mid-level (which results in a greyscale image) and played with the 16×16 luma prediction modes. When implementing an extremely naive algorithm to decide which 16×16 prediction mode would be the best for a particular block, this is what the program produced :

  
  
  

  For fun, here is what the image encodes to when forcing various prediction modes :
  

  I think the DC-only prediction mode actually looks a little better than the image that the naive algorithm produced :

  
  
  

  Vertical 16×16 prediction, similar to the image from the last post (just in black and white) :
  

  
  
  

  Horizontal 16×16 prediction :
  

  
  
  

  This is the 16×16 prediction mode unique to VP8, the TrueMotion mode (based on On2/Duck’s very first video codec) :
  

  
  
  

  Wow, these encodings really bring down the cheerful tone of the original image.

  Next Steps
  I have little reason to believe that I am encoding and subsequently reconstructing the image correctly (i.e., error is likely propagating through the entire encoding). If I have time, the next step is to validate my reconstruction against the encoder. Then I need to get the entropy considerations correct so that I actually get some compression out of this format.

• RTSP stream escape 1 or 2 seconds in output video file

  20 février 2017, par A Sahra

  I am trying to capture RTSP video from network path (rtsp ://10.29.23.1/video) using ffmpeg framework

  When i capture the video the output video file generated with ffmpeg is very low in quality and also it escape 1 or 2 seconds after each 5 seconds of the source video

  The command that i am running is :

  >#ffmpeg -i rtsp://10.20.2.2/aerovid -vcodec libx264 -framerate 5 -f mp4 public/out.mp4
  
  Log:after running above command:
  
  [h264 @ 0x2b75640] P sub_mb_type 32 out of range at 16 1464 bitrate=226.8kbits/s dup=30 drop=0 speed=3.27x 
  
  [h264 @ 0x2b75640] error while decoding MB 16 14 
  
  [h264 @ 0x2b75640] concealing 402 DC, 402 AC, 402 MV errors in P frame 
  
  [h264 @ 0x2b75640] mb_type 52 in P slice too large at 0 379 bitrate=239.0kbits/s dup=48 drop=0 speed=1.65x 
  
  [h264 @ 0x2b75640] error while decoding MB 0 3 
  
  [h264 @ 0x2b75640] concealing 869 DC, 869 AC, 869 MV errors in P frame 
  
  [h264 @ 0x2b75640] out of range intra chroma pred mode 
  
  [h264 @ 0x2b75640] error while decoding MB 34 1 
  
  [h264 @ 0x2b75640] concealing 917 DC, 917 AC, 917 MV errors in P frame 
  
  [h264 @ 0x2b75640] P sub_mb_type 9 out of range at 9 5 
  
  [h264 @ 0x2b75640] error while decoding MB 9 5 
  
  [h264 @ 0x2b75640] concealing 778 DC, 778 AC, 778 MV errors in P frame 
  
  [h264 @ 0x2b75640] negative number of zero coeffs at 9 1507 bitrate= 288.7kbits/s dup=50 drop=0 speed=1.37x 
  
  [h264 @ 0x2b75640] error while decoding MB 9 15 
  
  [h264 @ 0x2b75640] concealing 368 DC, 368 AC, 368 MV errors in P frame 
  
  [h264 @ 0x2b75640] out of range intra chroma pred mode 
  
  [h264 @ 0x2b75640] error while decoding MB 12 3 
  
  [h264 @ 0x2b75640] concealing 857 DC, 857 AC, 857 MV errors in P frame 
  
  [h264 @ 0x2b75640] mb_type 53 in P slice too large at 38 6 
  
  [h264 @ 0x2b75640] error while decoding MB 38 6 
  
  [h264 @ 0x2b75640] concealing 708 DC, 708 AC, 708 MV errors in P frame    
  
  Invalid UE golomb code 
  
  [h264 @ 0x2b75640] cbp too large (3199971767) at 28 12 
  
  [h264 @ 0x2b75640] error while decoding MB 28 12 
  
  [h264 @ 0x2b75640] concealing 472 DC, 472 AC, 472 MV errors in P frame

  What is the reason and how to solve it please ?