Recherche avancée

Sur d’autres sites (11442)

• 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.

• compile own ffmpeg filter

  20 juin 2023, par lfk

  I'm trying compile my own ffmpeg filter using official tutorial. My filter uses C++ code. I made header file and adapted my C++ function definition for C. Now I'm trying compile with command make -j<libavfilter> ffmpeg</libavfilter>, but receiving an error message

  


  


  gcc -Llibavcodec -Llibavdevice -Llibavfilter -Llibavformat
-Llibavresample -Llibavutil -Llibpostproc -Llibswscale -Llibswresample -Wl,—as-needed -Wl,-z,noexecstack -Wl,—warn-common -Wl,-rpath-link=libpostproc:libswresample:libswscale:libavfilter:libavdevice:libavformat:libavcodec:libavutil:libavresample
-o ffmpeg_g fftools/ffmpeg_opt.o fftools/ffmpeg_filter.o fftools/ffmpeg_hw.o fftools/cmdutils.o fftools/ffmpeg.o -lavdevice
-lavfilter -lavformat -lavcodec -lswresample -lswscale -lavutil -lm -pthread -lm -lm -lz -pthread -lm -lz -lm -lm -pthread -lm libavfilter/libavfilter.a(vf_foobar.o) : In function `filter_frame' :
/home/joeyes/ffmpeg_sources/ffmpeg/libavfilter/vf_foobar.c:302 :
undefined reference to MyFunction.c
collect2 : ld returned 1 exit status
*** [ffmpeg_g] Error 1

  


  


  For compilation I added OBJS-$(CONFIG_FOOBAR_FILTER) += vf_foobar.o MyCode.o to /libavfilter/makefile

  


  Also I put MyCode.h & MyCode.cpp to /libavfilter folder

  


• Xamarin Mac FFmpeg launch path not accessible

  25 mars 2024, par Tecnopresley

  I have a Xamarin Forms project with Mac support and I am trying to implement FFmpeg, so I have downloaded the Static build from its official page and added it as in the resources folder of the Mac project with the build action in Content, then I have created a service that will basically remove the audio from a video that I indicate in a path with a FFmpeg command, to do the service I have based on the following answer and I have adapted it to C # :
https://stackoverflow.com/a/37422688/8496520

  


  The problem is that when I try to execute the command I get the following error :

  


  "NSInvalidArgumentException: launch path not accessible"


  


  And I can't find out why this happens, I use the following code in the service (The error occurs when calling the Launch () method of the NSTask) :

  


  public void ExecuteFFmpeg()
{
    try
    {
        var launchPath = NSBundle.MainBundle.PathForResource("ffmpeg", ofType: "");
        var compressTask = new NSTask();
        compressTask.LaunchPath = launchPath;
        compressTask.Arguments = new string[] {
            "-i",
            "downloads/test.mp4",
            "-c",
            "copy",
            "-an",
            "nosound.mp4" };
        compressTask.StandardInput = NSFileHandle.FromNullDevice();
        compressTask.Launch();
        compressTask.WaitUntilExit();
    }
    catch (Exception ex)
    {

    }