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• Audio decoding using ffms2(ffmegsource)

  1er mai 2013, par praks411

  I'm using ffms2(ffmpegsource) a wrapper around libav to get video and audio frame from a file.
  Video decoding is working fine. However I'm facing some issues with audio decoding.
  FFMS2 provide a simple function FFMS_GetAudio(FFMS_AudioSource *A, void *Buf, int64_t Start, int64_t Count, FFMS_ErrorInfo *ErrorInfo); api to get the decoded buffer. The decoded data is return in buffer provided by user.

  For single channel the data is interpretation is straight forward with data byte starting from first location of user buffer. However when it comes to two channel there are two possibilities the decoded data could be planar or interleaved depending upon sample format return by FFMS_GetAudioProperties. In my case the sample format is always planar which means that decoded data will in two sperate data plane data[0] and data[1]. And this is what is explained by libav/ffmpeg and also by portaudio which consider planar data to be in two separate data plane.

  However FFMS_GetAudio just take single buffer from user. So can I assume for planar data
  data[0] = buf, data[1] = buf + offset, where offset is half the length of buffer return by FFMS_GetAudio.

  FFMS does not provide any good document for this interpretation. It would be great help if some can provide more information on this.

• CANNOT LINK EXECUTABLE error with required libs loaded. How to link them properly ? [duplicate]

  4 avril 2013, par dentex

  This question already has an answer here :

  • Android NDK - Library not found CANNOT LINK EXECUTABLE - how to set LD_LIBRARY_PATH ?
    

    1 answer

  edit : I'm aware of the possible duplicate, but the answer it's not directly applicable. I'm using ProcessBuilder and not Runtime.getRuntime().exec :

  public int execProcess(List<string> cmds, ShellUtils.ShellCallback sc) {    
  
      StringBuilder cmdlog = new StringBuilder();
  
      for (String cmd : cmds) {
  
           cmdlog.append(&#39; &#39;);
  
      }
  
      Utils.logger("v", cmdlog.toString(), DEBUG_TAG);
  
  
  
      ProcessBuilder pb = new ProcessBuilder();
  
      pb.directory(mBinFileDir);
  
      pb.command(cmds);
  
  
  
      Process process = null;
  
      int exitVal = 1; // Default error
  
      try {
  
          process = pb.start();
  
  
  
          StreamGobbler errorGobbler = new
  
          StreamGobbler(process.getErrorStream(), "ERROR", sc);
  
  
  
          StreamGobbler outputGobbler = new
  
          StreamGobbler(process.getInputStream(), "OUTPUT", sc);
  
  
  
          errorGobbler.start();
  
          outputGobbler.start();
  
  
  
          exitVal = process.waitFor();
  
  
  
          sc.processComplete(exitVal);
  
  
  
       } catch (Exception e) {
  
           Log.e(DEBUG_TAG, "Error executing ffmpeg command!", e);
  
       } finally {
  
           if (process != null) {
  
               Utils.logger("w", "destroyng process", DEBUG_TAG);
  
               process.destroy();
  
           }
  
      }
  
      return exitVal;
  
  }
  
  </string>

  ---

  I have two versions on FFmpeg compiled for android : with and without liblame enabled.

  When I load in /data/data/<>/app_bin/ the FFmpeg binary compiled with NO lame support, it extracts audio from video without an issue. But when I use the one with lame support enabled, I get the error below into the log.

  Required libs, also compiled for android, are correctly loaded when shipped into the libs project folder with System.loadLibrary("lame").

  I was wondering if there is something else to do in order to properly make the FFmpeg binary find the libs.
  Those are the same libs given to the NDK to build the FFmpeg binary.

  D/dalvikvm(13741): Trying to load lib /data/app-lib/<>/liblame.so 0x40ffed08
  
  D/dalvikvm(13741): Added shared lib /data/app-lib/<>/liblame.so 0x40ffed08
  
  D/dalvikvm(13741): No JNI_OnLoad found in /data/app-lib/<>/liblame.so 0x40ffed08, skipping init
  
  D/FfmpegController(13741): Trying to chmod '/data/data/<>/app_bin/ffmpeg' to: 755
  
  V/FfmpegController(13741): /data/data/<>/app_bin/ffmpeg -y -i /storage/sdcard0/Download/video.webm -vn -acodec copy /storage/sdcard0/Download/audio.ogg 
  
  >>>>>> ---------- <<<<<<
  
  D/DownloadsService(13741): soinfo_link_image(linker.cpp:1673): could not load library "liblame.so" needed by "/data/data/<>/app_bin/ffmpeg"; caused by load_library(linker.cpp:771): library "liblame.so" not foundCANNOT LINK EXECUTABLE
  
  >>>>>> ---------- <<<<<<
  
  I/DownloadsService(13741): FFmpeg process exit value: 255

  I'm not attaching code because it's fairly straightforward :

  • download the FFmpeg binary (it's not shipped with the app) ;
  • copy the binary from the download folder to /data/data/<>/app_bin/ ;
  • chmod 755 ;
  • execute from there and read the output.

  Please comment if something else is required.

• FFmpeg detecting the first frame after a commercial

  5 novembre 2013, par William Joe Baldwin

  I've been searching for a way to detect the very first frame after a commercial in FFmpeg.
  My recorder records TV shows, approximately 1 second before the sequence.
  Therefore the video file starts with few frames of the commercial.

  By checking the page below, it seems there is a way to detect scene changes :

  Extract Thumbnails of Every Camera Change on a Video File

  Does anyone know a way to rewrite the code from the link to get the first scene change as frame count ?

  Thanks !