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• Anomalie #4638 (Nouveau) : la constante _LEGACY_ACTIVE_IMG_DOC_EMB nécessite des modèles em...

  27 janvier 2021, par cy_altern -

  La constante _LEGACY_ACTIVE_IMG_DOC_EMB qui a été introduite par https://git.spip.net/spip/medias/commit/af1ba6cce5a5c8760e682e8b7fc872d076a87729 permet de faire l’appel direct aux modèle , et à la place de l’aiguillage selon le champs media qui le remplace en 3.3.
  ...sauf que le commit "fondateur" du nouveau système, https://git.spip.net/spip/medias/commit/fa13018a9ef63c633e78da253106867d6bac8a78, avait supprimé les fichiers modeles\doc.html, modeles\img.html et modeles\emb.html du plugin medias.
  Donc à moins d’apporter ces modèle via un plugin/squelette, l’activation de cette constante fait planter les raccourcis , et (ils ne sont tout simplement pas interprétés comme n’importe quel appel de modèle n’existant pas)

  Faut il restaurer les fichier doc.html, img.html et emb.html tant que cette constante existe (à priori au moins pour la version 3.3) ou faut il simplement le signaler dans la doc de la constante (avec éventuellement indication d’aller récupérer ces fichiers dans le dépot de la version 3.2) ?

• Anomalie #3227 : Bug date de publication

  17 septembre 2014, par 毎日 erational -

  quelqu’un sur le forum http://forum.spip.net/fr_258722.html signale une erreur de type avec le mktime

• How to extract motion vectors from h264 without a full decode on the CPU

  25 septembre 2020, par Adrian May

  I'm trying to use my nose as a pointing device. The plan is to encode the video stream from a webcam pointed at my face as h264 or the like, get the motion vectors, cook the numbers a bit and chuck them into /dev/uinput to make the mouse pointer move about. The uinput bit was easy.

  


  This has to work with zero discernable latency. This, for instance :

  


  #!/bin/bash
[ -p pipe.mkv ] || mkfifo pipe.mkv
ffmpeg -y -rtbufsize 1M -s 640x360 -vcodec mjpeg -i /dev/video0 -c h264_nvenc pipe.mkv &
ffplay -flags2 +export_mvs -vf codecview=mv=pf+bf+bb pipe.mkv


  


  shows that the vectors are there but with a latency of several seconds which is unusable in a mouse. I know that the first ffmpeg step is working very fast by using the GPU, so either the pipe or the h264 decode in the second step is introducing the latency.

  


  I tried MV Tractus (same as mpegflow I think) in a similar pipe arrangement and it was also very slow. They do a full h264 decode on the CPU and I think that's the problem cos I can see them imposing a lot of load on one CPU. If the pipe had caused the delay by buffering badly then the CPU wouldn't have been loaded. I guess ffplay also did the decoding on the CPU and I couldn't persuade it not to, but it only wants to draw arrows which are no use to me.

  


  I think there are several approaches, and I'd like advice on which would be best, or if there's something even better I don't know about. I could :

  


  

  • Decode in hardware and get the motion vectors. So far this has failed. I tried combining ffmpeg's extract_mvs.c and hw_decode.c samples but no motion vectors turn up. vdpau is the only decoder I got working on my linux box. I have a nvidia gpu.

  


  • Do a minimal parse of the h264 to fish out the motion vectors only, ignoring all the other data. I think this would mean putting some kind of "motion only" option in libav's parser, but I'm not at all familiar with that code.

  


  • Find some other h264 parsing library that has said option and also unpacks the container.

  


  • Forget about hardware accelerated encoding and use a stripped down encoder to make only the motion vectors on either CPU or GPU. I suspect this would be slow cos I think calculating the motion vectors is the hardest part of the algorithm.

  


  


  I'm tending towards the second option but I need some help figuring out where in the libav code to do it.