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• How to generate a empty .wav file (duration = 0, no silence/blank .wav) in ffmpeg ?

  11 août 2023, par fishshrimp鱼虾爆栈

  Background

  


  We need to generate silence wav in our logic, and using the following ffmpeg command :

  


  ffmpeg -f lavfi -t $duration -i anullsrc=channel_layout=stereo:sample_rate=48000 -y $output 


  


  All is ok untile we got a excetion in production environment :

  


  Error generating silence audio, length: 0, target: xxxx.wav, 
error: av_interleaved_write_frame(): No space left on device 
[wav @ 0x681fb80] Filesize 1258523197518 invalid for wav, 
output file will be broken Error writing trailer of


  


  As in previous log, it's because -t 0 will cause the ffmpeg generating unlimited file untile it blows up the disk when $duration == 0, then exception.

  


  Question

  


  

  1. Why -t 0 don't generate a empty wav ?

  


  2. And how to generate a epmty .wav/audio file in ffmpeg.

  


  


  


  PS, I found it Objective C Generating (empty) WAV file , but I want do do it in ffmpeg. I only get the silence generating questions and haven't search any question about duration=0. May be it's too rare to meet in real condition ?

  


  


• CD-R Read Speed Experiments

  21 mai 2011, par Multimedia Mike — Science Projects, Sega Dreamcast

  I want to know how fast I can really read data from a CD-R. Pursuant to my previous musings on this subject, I was informed that it is inadequate to profile reading just any file from a CD-R since data might be read faster or slower depending on whether the data is closer to the inside or the outside of the disc.

  Conclusion / Executive Summary
  It is 100% true that reading data from the outside of a CD-R is faster than reading data from the inside. Read on if you care to know the details of how I arrived at this conclusion, and to find out just how much speed advantage there is to reading from the outside rather than the inside.

  Science Project Outline

  • Create some sample CD-Rs with various properties
  • Get a variety of optical drives
  • Write a custom program that profiles the read speed

  Creating The Test Media
  It’s my understanding that not all CD-Rs are created equal. Fortunately, I have 3 spindles of media handy : Some plain-looking Memorex discs, some rather flamboyant Maxell discs, and those 80mm TDK discs :

  
  
  

  My approach for burning is to create a single file to be burned into a standard ISO-9660 filesystem. The size of the file will be the advertised length of the CD-R minus 1 megabyte for overhead— so, 699 MB for the 120mm discs, 209 MB for the 80mm disc. The file will contain a repeating sequence of 0..0xFF bytes.

  Profiling
  I don’t want to leave this to the vagaries of any filesystem handling layer so I will conduct this experiment at the sector level. Profiling program outline :

  • Read the CD-ROM TOC and get the number of sectors that comprise the data track
  • Profile reading the first 20 MB of sectors
  • Profile reading 20 MB of sectors in the middle of the track
  • Profile reading the last 20 MB of sectors

  Unfortunately, I couldn’t figure out the raw sector reading on modern Linux incarnations (which is annoying since I remember it being pretty straightforward years ago). So I left it to the filesystem after all. New algorithm :

  • Open the single, large file on the CD-R and query the file length
  • Profile reading the first 20 MB of data, 512 kbytes at a time
  • Profile reading 20 MB of sectors in the middle of the track (starting from filesize / 2 - 10 MB), 512 kbytes at a time
  • Profile reading the last 20 MB of sectors (starting from filesize - 20MB), 512 kbytes at a time

  Empirical Data
  I tested the program in Linux using an LG Slim external multi-drive (seen at the top of the pile in this post) and one of my Sega Dreamcast units. I gathered the median value of 3 runs for each area (inner, middle, and outer). I also conducted a buffer flush in between Linux runs (as root : 'sync; echo 3 > /proc/sys/vm/drop_caches').

  LG Slim external multi-drive (reading from inner, middle, and outer areas in kbytes/sec) :

  • TDK-80mm : 721, 897, 1048
  • Memorex-120mm : 1601, 2805, 3623
  • Maxell-120mm : 1660, 2806, 3624

  So the 120mm discs can range from about 10.5X all the way up to a full 24X on this drive. For whatever reason, the 80mm disc fares a bit worse — even at the inner track — with a range of 4.8X - 7X.

  Sega Dreamcast (reading from inner, middle, and outer areas in kbytes/sec) :

  • TDK-80mm : 502, 632, 749
  • Memorex-120mm : 499, 889, 1143
  • Maxell-120mm : 500, 890, 1156

  It’s interesting that the 80mm disc performed comparably to the 120mm discs in the Dreamcast, in contrast to the LG Slim drive. Also, the results are consistent with my previous profiling experiments, which largely only touched the inner area. The read speeds range from 3.3X - 7.7X. The middle of a 120mm disc reads at about 6X.

  Implications
  A few thoughts regarding these results :

  • Since the very definition of 1X is the minimum speed necessary to stream data from an audio CD, then presumably, original 1X CD-ROM drives would have needed to be capable of reading 1X from the inner area. I wonder what the max read speed at the outer edges was ? It’s unlikely I would be able to get a 1X drive working easily in this day and age since the earliest CD-ROM drives required custom controllers.
  • I think 24X is the max rated read speed for CD-Rs, at least for this drive. This implies that the marketing literature only cites the best possible numbers. I guess this is no surprise, similar to how monitors and TVs have always been measured by their diagonal dimension.
  • Given this data, how do you engineer an ISO-9660 filesystem image so that the timing-sensitive multimedia files live on the outermost track ? In the Dreamcast case, if you can guarantee your FMV files will live somewhere between the middle and the end of the disc, you should be able to count on a bitrate of at least 900 kbytes/sec.

  Source Code
  Here is the program I wrote for profiling. Note that the filename is hardcoded (#define FILENAME). Compiling for Linux is a simple 'gcc -Wall profile-cdr.c -o profile-cdr'. Compiling for Dreamcast is performed in the standard KallistiOS manner (people skilled in the art already know what they need to know) ; the only variation is to compile with the '-D_arch_dreamcast' flag, which the default KOS environment adds anyway.

  PLAIN TEXT

  C :

  1. #ifdef _arch_dreamcast
  2.   #include <kos .h>
  3.  
  4.   /* map I/O functions to their KOS equivalents */
  5.   #define open fs_open
  6.   #define lseek fs_seek
  7.   #define read fs_read
  8.   #define close fs_close
  9.  
  10.   #define FILENAME "/cd/bigfile"
  11. #else
  12.   #include <stdio .h>
  13.   #include <sys /types.h>
  14.   #include </sys><sys /stat.h>
  15.   #include </sys><sys /time.h>
  16.   #include <fcntl .h>
  17.   #include <unistd .h>
  18.  
  19.   #define FILENAME "/media/Full disc/bigfile"
  20. #endif
  21.  
  22. /* Get a current absolute millisecond count ; it doesn’t have to be in
  23. * reference to anything special. */
  24. unsigned int get_current_milliseconds()
  25. {
  26. #ifdef _arch_dreamcast
  27.   return timer_ms_gettime64() ;
  28. #else
  29.   struct timeval tv ;
  30.   gettimeofday(&tv, NULL) ;
  31.   return tv.tv_sec * 1000 + tv.tv_usec / 1000 ;
  32. #endif
  33. }
  34.  
  35. #define READ_SIZE (20 * 1024 * 1024)
  36. #define READ_BUFFER_SIZE (512 * 1024)
  37.  
  38. int main()
  39. {
  40.   int i, j ;
  41.   int fd ;
  42.   char read_buffer[READ_BUFFER_SIZE] ;
  43.   off_t filesize ;
  44.   unsigned int start_time, end_time ;
  45.  
  46.   fd = open(FILENAME, O_RDONLY) ;
  47.   if (fd == -1)
  48.   {
  49.     printf("could not open %s\n", FILENAME) ;
  50.     return 1 ;
  51.   }
  52.   filesize = lseek(fd, 0, SEEK_END) ;
  53.  
  54.   for (i = 0 ; i <3 ; i++)
  55.   {
  56.     if (i == 0)
  57.     {
  58.       printf("reading inner 20 MB...\n") ;
  59.       lseek(fd, 0, SEEK_SET) ;
  60.     }
  61.     else if (i == 1)
  62.     {
  63.       printf("reading middle 20 MB...\n") ;
  64.       lseek(fd, (filesize / 2) - (READ_SIZE / 2), SEEK_SET) ;
  65.     }
  66.     else
  67.     {
  68.       printf("reading outer 20 MB...\n") ;
  69.       lseek(fd, filesize - READ_SIZE, SEEK_SET) ;
  70.     }
  71.     /* read 20 MB ; 40 chunks of 1/2 MB */
  72.     start_time = get_current_milliseconds() ;
  73.     for (j = 0 ; j <(READ_SIZE / READ_BUFFER_SIZE) ; j++)
  74.       if (read(fd, read_buffer, READ_BUFFER_SIZE) != READ_BUFFER_SIZE)
  75.       {
  76.         printf("read error\n") ;
  77.         break ;
  78.       }
  79.     end_time = get_current_milliseconds() ;
  80.     printf("%d - %d = %d ms => %d kbytes/sec\n",
  81.       end_time, start_time, end_time - start_time,
  82.       READ_SIZE / (end_time - start_time)) ;
  83.   }
  84.  
  85.   close(fd) ;
  86.  
  87.   return 0 ;
  88. }

• Matomo SSO options and why is it useful ?

  8 novembre 2017, par Matomo Core Team — Plugins

  Bored with typing again and again different logins and passwords for each service you have access to ? Would you like to add hundreds or thousands of users with different roles to your Matomo (Piwik) at once ? Would you like to save time and effort of managing your users while increasing the security in your business ? Guess what, Matomo has come up with great features to do just that.

  But what is a SSO ?

  Before introducing you to new Matomo (Piwik) features, let me explain what a SSO is.
  SSO is the acronym for Single Sign On. As its name suggests this authentication process allows a user to access multiple applications with one set of login credentials.

  Advantages of using a SSO are numerous :

  • improving security, for example when an employee is leaving your company, how can you check that all his credentials have been removed ?
  • reducing employees time-wasters such as having to enter logins/passwords each time.
  • providing a centralized database for administrators. They can then easily manage permissions of all employees saving them heaps of time.
  • reduces support costs related to authentication / accounts management.

  In order to provide SSO options, two Matomo (Piwik) plugins have been developed and are available on the marketplace :

  • SAML
  • LDAP

  SAML

  

  SAML stands for “Security Assertion Markup Language”, it is a standard in order to exchange authentication and authorization between an identity provider (OneLogin, Okta, Ping Identity, ADFS, Google, Salesforce, SharePoint…) and a service provider.
  An identity provider is an online service that authenticates users on the Internet by using security tokens.

  Are you wondering if your business or organization is using any of these providers ? We recommend to ask your operations team or sysadmin.

  At InnoCraft, we developed a plugin in order to allow SSO with SAML for Matomo (Piwik). It can ensure consistent access control across the enterprise and external providers, potentially reducing support costs related to authentication and accounts management.

  The installation process is straightforward. All you need is to get the SAML premium feature from the marketplace. Once installed, you will access the SAML configuration interface through the admin where you can configure various settings :

  • SAML Status
  • Identity Provider (Entity ID, SSO endpoint info, Public x509 certificate)
  • Just-in-time provisioning and Mapping attributes
  • Access Synchronization
  • Advanced settings

  

  From there you will need to follow our detailed documentation to have it up and running :
  https://matomo.org/docs/login-saml/.
  Once finished, you will then be able to use SAML to authenticate to your Matomo (Piwik) account :

  

  As all premium features, SAML is eligible to a 30-day period money back guarantee, so do not hesitate to have it a try.

  LDAP

  

  LDAP stands for Lightweight Directory Access Protocol. As its names implies LDAP is a directory, hosted on a server, which organizes the data about people in your company.
  Thanks to the LDAP plugin, Matomo (Piwik) can be connected to your LDAP infrastructure and then use all its power in order to give each individual an access with different rights according to their needs.

  Let’s say that you have 1,000 employees within a company and they all need right now an access to the analytics reports in Matomo (Piwik) with different roles. This is what LDAP can do.

  Moreover if your business or organization is already using LDAP, we recommend using the LDAP connector for Matomo (Piwik) for better security, to stop wasting time of your users and sysadmins, and to reduce the costs related to account management.

  You understood it well. LDAP is a plugin which saves a LOT of time within an organization. Here is a preview of the settings part :

  

  LDAP has been developed by the Matomo (Piwik) core team and is available as a Free plugin on the marketplace.

  Try it now within the marketplace

  If you are surprised by the possibilities that Matomo (Piwik) is offering in terms of plugins, the good news is that many other plugins are waiting for you on the marketplace. Check out our premium marketplace which offers state-of-the-art plugins to get the most out of Matomo.

  And if you are a developer feel free to create your own plugin, a detailed documentation is available at : https://developer.matomo.org/guides/getting-started-part-1.