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• Anomalie #3991 : Erreur compression CSS et base64

  29 août 2017, par tcharlss (*´_ゝ｀)

  La ligne fautive se trouve ici : https://zone.spip.org/trac/spip-zone/browser/_core_/plugins/compresseur/inc/compresseur_minifier.php#L100

  // zero est zero, quelle que soit l’unite (sauf pour % car casse les @keyframes cf https://core.spip.net/issues/3128)
  $contenu = preg_replace("/([^0-9.]0)(em|px|pt)/ms", "$1", $contenu) ;
  

  Ça cherche le nombre zéro précédé de n’importe quel caractère (autre qu’un chiffre) ou d’un point.
  Du coup ça peut matcher avec les data URIs :
  

  @font-facefont-family :’spip’ ;src:url("data:application/font-woff ;base64,abc0pxyz") ;
  

  Pour éviter ce souci, on pourrait préciser exactement quels caractères peuvent précéder le zéro pour considérer qu’il s’agit d’une unité. On peut avoir :

  1) deux points
  

  font-size:0px ;
  

  2) un ou plusieurs espaces
  

  font-size : 0px ;
  font-size : calc(10px + 0px) ;
  

  3) une parenthèse dans le cas de calc()
  

  font-size : calc(0px) ;
  

  4) Autres unités

  À noter qu’il y a aussi pas mal d’autres unités qui ne sont pas prises en compte dans la regex actuelle : https://www.w3schools.com/cssref/css_units.asp
  

  rem ex pc
  vh vw vmin vmax 
  cm mm in
  ch 
  

  ---

  Ce qui donne au final la regex suivante, qui laisse mes data URIs tranquilles :
  

  $contenu = preg_replace("/((?: :|\s+|\()0)(em|px|pt|rem|ex|pc|vh|vw|vmin|vmax|cm|mm|in|ch)/ms", "$1", $contenu) ;
  

• How to stream live h.264 (IP camera) video to browser ? (bonus : low bandwidth and latency)

  4 octobre 2018, par Ryan Griggs

  I need to stream live h.264-encoded video from an IP camera to the browser, while supporting all common browsers and mobile devices (i.e. Android, Firefox, Chrome, IE, Safari (Mac OS and iOS)), and while keeping bandwidth requirements and latency to a minimum.

  MPEG-DASH requires browser support for Media Source Extensions, which are NOT supported by iOS. So that’s out.

  HLS is only supported by Safari and Edge.

  Also DASH seems to impose a latency of several seconds, which is not preferable.

  I would like to be able to chunk the incoming h.264 data (i.e. fragmented MP4), pass the chunked data to the browser via Websockets, then dump the chunks into some sort of player as they arrive.

  Broadway and its forks are a javascript h.264 decoder, and there is a Broadway-stream project that supports streams instead of files, but the docs are poor and I can only find examples of streaming when the source is not live.

  The most pressing question is : how do I hand the "chunked data" to a player or Video HTML element as it arrives at the browser ?

  I think the ideal setup would be to

  1. Use ffmpeg to transcode the original video to a chunked format (fMP4)
  2. Pipe the chunked output to a Node JS app which emits each chunk out through a Websocket to all connected viewers
  3. Viewers’ browsers dump each incoming chunk into some sort of decoder which renders the video.

  I’m clear up to the point of handing the received chunks to a video decoder. How can that be done without depending on Media Source Extensions, and allowing viewers to join the stream at random times ?

• Extracting Metadata from a video file (.mkv) using FFmpeg

  14 avril 2023, par Ashutosh Singla

  I have a video file that contains 4 streams, 3 videos streams and one steam for metadata.

  


  Stream Info :

  


  Input #0, matroska,webm, from 'output_master.mkv':
Metadata:
title           : Azure Kinect
encoder         : libmatroska-1.4.9
creation_time   : 2021-05-20T12:11:15.000000Z
K4A_DEPTH_DELAY_NS: 0
K4A_WIRED_SYNC_MODE: MASTER
K4A_COLOR_FIRMWARE_VERSION: 1.6.110
K4A_DEPTH_FIRMWARE_VERSION: 1.6.79
K4A_DEVICE_SERIAL_NUMBER: 000123102712
K4A_START_OFFSET_NS: 298800000
Duration: 00:00:40.03, start: 0.000000, bitrate: 480934 kb/s

Stream #0:0(eng): Video: mjpeg (Baseline) (MJPG / 0x47504A4D), yuvj422p(pc, bt470bg/unknown/unknown), 2048x1536, SAR 1:1 DAR 4:3, 30 fps, 30 tbr, 1000k tbn (default)
Metadata:
  title           : COLOR
  K4A_COLOR_TRACK : 14499183330009048
  K4A_COLOR_MODE  : MJPG_1536P
Stream #0:1(eng): Video: rawvideo (b16g / 0x67363162), gray16be, 640x576, SAR 1:1 DAR 10:9, 30 fps, 30 tbr, 1000k tbn (default)
Metadata:
  title           : DEPTH
  K4A_DEPTH_TRACK : 429408169412322196
  K4A_DEPTH_MODE  : NFOV_UNBINNED
Stream #0:2(eng): Video: rawvideo (b16g / 0x67363162), gray16be, 640x576, SAR 1:1 DAR 10:9, 30 fps, 30 tbr, 1000k tbn (default)
Metadata:
  title           : IR
  K4A_IR_TRACK    : 194324406376800992
  K4A_IR_MODE     : ACTIVE
Stream #0:3: Attachment: none
Metadata:
  filename        : calibration.json
  mimetype        : application/octet-stream
  K4A_CALIBRATION_FILE: calibration.json


  


  I am using the below command to extract Stream #0:0, Stream #0:1, and Stream #0:2 by changing map 0:X.

  


  ffmpeg -i output_master.mkv -c copy -allow_raw_vfw 1 -map 0:0 temp_0.mkv 


  


  To extract the metadata from all the streams and store them in metadata.txt, I am using the command below :

  


  ffprobe -v quiet -show_format -show_streams -print_format json output_master.mkv > metadata.txt


  


  What should be the command to extract Stream #0:3 ? Any help would be appreciated.