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• On ALAC’s Open Sourcing

  1er novembre 2011, par Multimedia Mike — Codec Technology

  Apple open sourced their lossless audio codec last week. Pretty awesome ! I have a theory that, given enough time, absolutely every codec will be open source in one way or another.

  I know I shouldn’t bother reading internet conversation around any news related to multimedia technology. And if I do read it, I shouldn’t waste any effort getting annoyed about them. But here are some general corrections :

  • ALAC is not in the same league as — nor is it a suitable replacement for — MP3/AAC/Vorbis or any other commonly used perceptual audio codec. It’s not a matter of better or worse ; they’re just different families of codecs designed for different purposes.
  • Apple open sourced ALAC, not AAC– easy mistake, though there’s nothing to ‘open source’ about AAC (though people can, and will, argue about its absolute ‘open-ness’).
  • There’s not much technical room to argue between ALAC and FLAC, the leading open source lossless audio compressor. Both perform similarly in terms of codec speeds (screamingly fast) and compression efficiency (results vary slightly depending on source material).
  • Perhaps the most frustrating facet is the blithe ignorance about ALAC’s current open source status. While this event simply added an official “open source” status to the codec, ALAC has effectively been open source for a very long time. According to my notes, the ALAC decoding algorithm was reverse engineered in 2005 and added into FFmpeg in March of the same year. Then in 2008, Google — through their Summer of Code program — sponsored an open source ALAC encoder.

  From the multimedia-savvy who are versed in these concepts, the conversation revolves around which would win in a fight, ALAC or FLAC ? And who between Apple and FFmpeg/Libav has a faster ALAC decoder ? The faster and more efficient ALAC encoder ? I contend that these issues don’t really matter. If you have any experience working with lossless audio encoders, you know that they tend to be ridiculously fast to both encode and decode and that many different lossless codecs compress at roughly the same ratios.

  As for which encoder is the fastest : use whatever encoder is handiest and most familiar, either iTunes or FFmpeg/Libav.

  As for whether to use FLAC or ALAC — if you’ve already been using one or the other for years, keep on using it. Support isn’t going to vanish. If you’re deciding which to use for a new project, again, perhaps choose based on software you’re already familiar with. Also, consider hardware support– ALAC enjoys iPod support, FLAC is probably better supported in a variety of non-iPod devices, though that may change going forward due to this open sourcing event.

  For my part, I’m just ecstatic that the question of moral superiority based on open source status has been removed from the equation.

  Code-wise, I’m interested in studying the official ALAC code to see if it has any corner-case modes that the existing open source decoders don’t yet account for. The source makes mention of multichannel (i.e., greater than stereo) configurations, but I don’t know if that’s in FFmpeg/Libav.

• How to generate SDP file from FFMPEG

  20 novembre 2016, par MobilityLab

  So, I have been working with FFMPEG on a project that involves streaming video from one computer to another across the internet with RTP. I want to take that into ffmpeg and use ffserver to display it on a local network.

  As I understand it, you need to have a SDP information so that the receiving ffmpeg instance can interpret the RTP stream. Despite what webpages say, I can not find the SDP information in the information printed to the console.

  How can I force the transmitting ffmpeg instance to output the SDP information so that I can use it to configure my receiving end ?

  Right now, I am testing on Windows 7, but the final solution will be on linux.

  The command I’m running for testing is

  ffmpeg -fflags +genpts -i files\2005-SFSD-sample-mpeg1.mpg -threads 0 -r 10 -g 45
  
  -s 352x240 -deinterlace -y 2005.mp4 -an -threads 0 -r 10 -g 45 -s 352x240 
  
  -deinterlace -f rtp rtp://192.168.200.198:9008

  My ffmpeg information is...

  ffmpeg version 0.8, Copyright (c) 2000-2011 the FFmpeg developers built on Jun 23 2011 14:22:23 with gcc 4.5.3 
  
  configuration: 
  
  --disable-static  
  
  --enable-shared 
  
  --enable-gpl  
  
  --enable-version3 
  
  --enable-memalign-hack  
  
  --enable-runtime-cpudetect 
  
  --enable-avisynth 
  
  --enable-bzlib 
  
  --enable-frei0r 
  
  --enable-libopencore-amrnb 
  
  --enable-libopencore-amrwb 
  
  --enable-libfreetype 
  
  --enable-libgsm 
  
  --enable-libmp3lame 
  
  --enable-libopenjpeg 
  
  --enable-librtmp 
  
  --enable-libschroedinger 
  
  --enable-libspeex 
  
  --enable-libtheora 
  
  --enable-libvorbis 
  
  --enable-libvpx 
  
  --enable-libx264 
  
  --enable-libxavs 
  
  --enable-libxvid 
  
  --enable-zlib 
  
  --disable-outdev=sdl 
  
    libavutil    51.  9. 1 / 51.  9. 1 
  
    libavcodec   53.  7. 0 / 53.  7. 0 
  
    libavformat  53.  4. 0 / 53.  4. 0 
  
    libavdevice  53.  1. 1 / 53.  1. 1 
  
    libavfilter   2. 23. 0 /  2. 23. 0 
  
    libswscale    2.  0. 0 /  2.  0. 0 
  
    libpostproc  51.  2. 0 / 51.  2. 0 

• Anomalie #2916 : BOUCLE HIERARCHIE et critère { !titre_mot}

  7 décembre 2012, par realet RealET

  Un peu d’histoire : http://archives.rezo.net/archives/spip-dev.mbox/7JRXPODAC5JSSFV5DINM6N44HDHYPHGR/ : r15834 hhttp://article.gmane.org/gmane.comp.web.spip.devel/29841 : documentation initiale de 2005 : renverser la hiérarchie est toujours enrichissant (...)