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• Anomalie #3444 : Nombreuses erreurs dans les log avec une instal en SQLite 2

  28 mars 2016, par Franck Dalot

  je viens de faire 2 tests en SPIP 3.1.1 [22968]
  PHP 5.3.29
  SQLite 2
  Alors pour info, il y a eu des changements depuis la création du ticket ! :-) Faudrait sans doute faire un changement de titre du ticket du coup ou en refaire des nouveaux...

  Premier test avec aucun préfix de table particulier et en faisant un article bidon
  - Maintenant, je peux ouvrir le fichier sqlite et le site semble ok, mais par contre, si je regarde la sauvegarde, les tables sont vides, pourtant, si je regarde dans le menu "développement" l’article est dans la base, il est bien dans ecrire/ ?exec=vertebres&table=spip_articles

  Deuxième test avec un préfixe de table particulier (test)
  - Je peux ouvrir le fichier sqlite, le site semble ok, mais si je vais dans le menus "développement" je ne peux faire de consultation de la bdd car cela me dit dans une boite "Aucun squelette prive/vertebres:test_articles n’est disponible..."
  Possible que cela soit un autre bug qui demanderait un autre ticket rien que pour lui ?!
  Je t’envoi les deux sauvegardes par mail

• Making Sure The PNG Gets There

  14 juin 2013, par Multimedia Mike — General

  Rewind to 1999. I was developing an HTTP-based remote management interface for an embedded device. The device sat on an ethernet LAN and you could point a web browser at it. The pitch was to transmit an image of the device’s touch screen and the user could click on the picture to interact with the device. So we needed an image format. If you were computing at the time, you know that the web was insufferably limited back then. Our choice basically came down to GIF and JPEG. Being the office’s annoying free software zealot, I was championing a little known up and coming format named PNG.

  So the challenge was to create our own PNG encoder (incorporating a library like libpng wasn’t an option for this platform). I seem to remember being annoyed at having to implement an integrity check (CRC) for the PNG encoder. It’s part of the PNG spec, after all. It just seemed so redundant. At the time, I reasoned that there were 5 layers of integrity validation in play.

  I don’t know why, but I was reflecting on this episode recently and decided to revisit it. Here are all the encapsulation layers of a PNG file when flung over an ethernet network :

  
  
  

  So there are up to 5 encapsulations for the data in this situation. At the innermost level is the image data which is compressed with the zlib DEFLATE method. At first, I thought that this also had a CRC or checksum. However, in researching this post, I couldn’t find any evidence of such an integrity check. Further, I don’t think we bothered to compress the PNG data in this project long ago. It was a small image, monochrome, and transferring via LAN, so the encoder could get away with signaling uncompressed data.

  The graphical data gets wrapped up in a PNG chunk and all PNG chunks have a CRC. To transmit via the network, it goes into a TCP frame, which also has a checksum. That goes into an IP packet. I previously believed that this represented another integrity check. While an IP frame does have a checksum, the checksum only covers the IP header and not the payload. So that doesn’t really count towards this goal.

  Finally, the data gets encapsulated into an ethernet frame which has — you guessed it — a CRC.

  I see that other link layer protocols like PPP and wireless ethernet (802.11) also feature frame CRCs. So I guess what I’m saying is that, if you transfer a PNG file over the network, you can be confident that the data will be free of any errors.

• FPS from RTSP stream info does not match actual framerate

  17 mai 2021, par Krapow

  I have a 25FPS RTSP stream coming from an IP-camera. I can successfully display the video stream. But when analyzing the stream with ffmpeg (ffprobe actually), I observe fewer frames per second rate :

  


  $ ffprobe -rtsp_transport tcp -i rtsp://camera_ip:554/stream -select_streams v:0 -show_frames -show_entries frame=coded_picture_number,pkt_pts_time -of csv=p=0
Stream #0:0: Video: h264 (Main), yuvj420p(pc, bt709, progressive), 640x480, 25 fps, 25 tbr, 90k tbn, 50 tbc
0.400000,0
0.080000,1
0.120000,2
0.200000,3
0.240000,4
0.320000,5
0.360000,6
0.440000,7
0.480000,8
0.560000,9
0.600000,10
0.680000,11
0.720000,12
0.800000,13
0.840000,14
0.920000,15
0.960000,16
1.040000,17
1.080000,18
1.160000,19
1.200000,20
1.280000,21
1.320000,22
1.400000,23
1.440000,24
1.520000,25
1.560000,26
1.640000,27
1.680000,28
1.760000,29
1.800000,30
1.880000,31
1.920000,32
2.000000,33


  


  We can clearly see the 80ms gap between some of the frames, resulting in a 16fps stream.

  


  I have observed the same framerate issue with GStreamer (printing information in the rtpjitterbuffer indicates the frame gap is sometimes 80ms and sometimes 40ms). But the weird thing is, I encountered the same issue with an HDMI-RJ45 decoder, and I doubt the same issue comes from 2 different devices.
I didn't get much more informations using -loglevel debug or trace.
Does anybody have an idea about what is going wrong in the stream ?

  


  (I used ffprobe 4.2.3 and the last "2021-05-09-git-8649f5dca6-full_build-www.gyan.dev" with the same results, and GStreamer 1.16.2 with a pipeline like "urisourcebin ! h264depay ! h264parse ! fakesink")

  


  EDIT : The camera skipping of frames was caused by the activation of a third stream in the options. I find it really weird that it skips exactly the same frames every seconds. However, I still haven't found the cause of the downrate on my RTSP encoder.
Anyway, this was actually hardware related and not software related.