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• change wav, aiff or mov audio sample rate of MOV or WAV WITHOUT changing number of samples

  6 mars 2013, par John Pilgrim

  I need a very precise way to speed up audio.
  I am preparing films for OpenDCP, an open-source tool to make Digital Cinema Packages, for screening in theaters.
  My source files are usually quicktime MOV files at 23.976fps with 48.000kHz audio.
  Sometimes my audio is a separate 48.000kHz WAV.
  (FWIW, the video frame rate of the source is actually 24/100.1 frames per second, which is a repeating decimal.)

  The DCP standard is based around a 24.000fps and 48.000kHz program, so the audio and video of the source need to be sped up.
  The image processing workflow inherently involves converting the MOV to a TIF sequence, frame-per-frame, which is then assumed to be 24.000fps, so I don't have to get involved in the internals of the QT Video Media Handler.

  But speeding up the audio to match is proving to be difficult. Most audio programs cannot get the number of audio samples to line up with the retimed image frames. A 0.1% speed increase in Audacity results in the wrong number of samples. The only pathway that I have found that works is to use Apple Cinema Tools to conform the 23.976fps/48.000kHz MOV to 24.000fps/48.048kHz (which it does by changing the Quicktime headers) and then using Quicktime Player to export the audio from that file at 48.000kHz, resampling it. This is frame accurate.

  So my question is : are there settings in ffmpeg or sox that will precisely speed up the audio in a MOV or in a WAV or AIFF precisely ? I would like a cross platform solution, so I am not dependent on Cinema Tools, which is only MacOS.

  I know this is a LOT of background. Feel free to ask clarifying questions !

• Unable to recognize text with 100 % accuracy in a jpg file using Tess4J

  21 février 2013, par sonali mishra

  I want to split a .flv video file into .jpg/png frames of good resolution & then want to recognize the character sequence in it using Tess4J tool (JNA wrapper around Tesseract).

  Currently I tried the ffmpeg command line tool to split the .flv video file into jpg images.The ffmpeg command I used is :

  ffmpeg -i myinput.flv myoutput%d.jpg

  It is giving me the output image having the detail :

  Image Dimensions : 1280 * 696

  Horizontal resolution : 96 dpi

  Vertical resolution : 96 dpi

  bit depth : 24

  My Problem is :
  I tried to recognize the characters in the video frames(jpg image files which i splitted) using the following code snippet using Tess4J, it is recognizing the characters, but not identifying with 100 % accuracy. It is adding some junk characters as well which is not there in the image.

  Java code snippet I am using :

  import java.io.BufferedWriter
  
  
  
  import java.io.File;
  
  
  
  import java.io.FileWriter;
  
  
  
  import java.io.IOException; 
  
  
  
  import net.sourceforge.tess4j.Tesseract;
  
  
  
  import net.sourceforge.tess4j.TesseractException;
  
  
  
  public class TesseractDemo {
  
  
  
  public static void main(String[] args) {
  
  
  
      File imageFile = new File("D:\\myinput1.jpg");
  
  
  
      Tesseract instance = Tesseract.getInstance();
  
  
  
      // Tesseract1 instance = new Tesseract1();
  
  
  
      try {
  
  
  
          String result = instance.doOCR(imageFile);
  
  
  
          System.out.println(result);
  
  
  
          // write in a file
  
          try {
  
              File file = new File("D:\\myoutput1.txt");
  
              BufferedWriter out = new BufferedWriter(new FileWriter(file));
  
              out.write(result);
  
              out.close();
  
          } catch (IOException ex) {
  
          }
  
  
  
      } catch (TesseractException ep) {
  
          System.err.println(ep.getMessage());
  
      }
  
  
  
  }

  }

  Note : In Tess4J site they have told that the image you are using for doing OCR should be of more than 200 dpi(dot per inch). How to get the jpg image of more than 200 dpi using ffmpeg ??

  Any body having any java code snippet or any suggestion in this regard please help.

• correcting captured dvb-t video from two different mpeg-ts sources

  17 février 2013, par Ondra Kocian

  I have captured same channel (two files - full multiplex of dvb-t - mpeg-ts) from different dvb-t transmitters :

  Transmitter-A.ts
  Transmitter-B.ts

  I would like to merge these streams to produce one perfect video of channel to correct failtures in signal from transmitter-B and transmitter-A - I know there are frame gaps lets say :

  Transmitter-A.ts 1:10-1:20
  Transmitter-B.ts 2:30-2:35

  Is there some existing tool to do so ? Do I have to go to the frame level of ts packet and compare them between streams(lets say find I-frames-will they fit ? And compare them) ? I hoped pts and dts timestamps would fit but didnt - is there some way to use pcr or any stamp in ts packet preventing me to go on frame level ?