FFmpeg build and run

How to build and run ffmpeg 0.8

1. download 0.8 ffmepg

2. Install libsdl libsdl-mix, using synaptic package manager

3 ./configure --enable-gpl --enable-nonfree --enable-pthreads --enable-shared --disable-yasm --enable-debug=3 --disable-stripping --prefix=/home/xgu/ffmpeg

4. make; make install;

5. cd /home/xgu/ffmpeg/bin

6. LD_LIBRARY_PATH=../lib ./ffmpeg -s 640x480 -f video4linux2 -i /dev/video0 -f mpegts -vcodec mpeg2video out1.mpeg

7. LD_LIBRARY_PATH=../lib ./ffplay  Some_Video_File

Video Audio Capture in Linux

Video
Webcam support in Linux is mainly provided by the Linux UVC Project's UVC driver.

The UVC driver implements the Video4Linux 2 (V4L2) API

The specification of V4L2 API can be found at http://v4l2spec.bytesex.org/

Example:
In ffmpeg, file libavdevice/v4l2.c
http://v4l2spec.bytesex.org/v4l2spec/capture.c

Command:
#To capture video
ffmpeg -f video4linux2 -i /dev/video0 out.mpeg


Audio
Ubuntu is using ALSA for audio input output

Command:
#To capture audio
ffmpeg -f alsa -ac 2 -i hw:0 alsaout.wav

#To get hardware info
arecord -l



Reference:
http://ffmpeg.org/ffmpeg-doc.html
http://www.ideasonboard.org/uvc/
https://help.ubuntu.com/community/Webcam
https://help.ubuntu.com/community/UVC
http://v4l2spec.bytesex.org/
http://www.alsa-project.org/

Encode PCM to M4A

ffmpeg -i audiobo.aiff -strict experimental  -acodec aac  -ab 64k -ar 22050 a.m4a

Encode PCM to MP3

To encode PCM data to MP3 in Ubuntu 11.04:

sudo apt-get build-dep ffmpeg

sudo apt-get install libmp3lame-dev libfaad-dev libx264-dev libfaac-dev libxvidcore-dev liba52-0.7.4 liba52-0.7.4-dev libdts-dev checkinstall

apt-get source ffmpeg

cd libav-*

./configure  --disable-debug --enable-libfaad --enable-libfaac --enable-gpl  --enable-nonfree --enable-libx264 --enable-libxvid --enable-pthreads --enable-libvorbis --enable-libmp3lame --enable-libtheora --enable-libgsm  --disable-debug --enable-shared --prefix=/usr

make

sudo checkinstall -D make install

ffmpeg -i audiobo.aiff -f mp3 -acodec libmp3lame -ab 64k -ar 22050 output.mp3

Reference:
https://wiki.ubuntu.com/ffmpeg
http://turanct.wordpress.com/2010/04/03/convert-aiff-to-mp3-with-ffmpeg-on-ubuntu/

Calculate Audio Level

How to calculate audio level from PCM sample data:

http://en.wikipedia.org/wiki/Root_mean_square
Sample Code

  protected void updateLevelAndPeak(ByteBuffer bytebuffer, int bufferLen) {
    int numFrame = bufferLen / frameSizeInBytes;
    long sampleSqureTotal = 0L;
    long peak = 0L;
    ShortBuffer shortbuffer = bytebuffer.asShortBuffer();
    for (int indexFrame = 0; indexFrame < numFrame; indexFrame++) {
      int sampleValue = 0;
      for (int indexChannel = 0; indexChannel < channels; indexChannel++) {
        sampleValue += shortbuffer.get(channels * indexFrame + indexChannel);
      }

      sampleValue /= channels;
      int k = Math.abs(sampleValue);
      sampleSqureTotal += sampleValue * sampleValue;
      if ((long) k > peak) {
        peak = k;
      }
    }

    currentLevel = numFrame <= 0 ? 0.0D : Math.sqrt(sampleSqureTotal / (long) numFrame);
    currentPeak = peak;
  }

Reference:
http://wiki.hydrogenaudio.org/index.php?title=Replaygain

How to make JSONP call in GWT

Example goes here:

String url3 = "https://ajax.googleapis.com/ajax/services/search/news?v=1.0&q=barack%20obama";
JsonpRequestBuilder jsonp = new JsonpRequestBuilder();

//jsonp.setCallbackParam("callback");
//gwt will generate a java script object of url "http://url_of_some_service?para=value%callback=_xxxx_onSuccess"
//the _xxxx_onSuccess points to below onSucess function.

jsonp.requestObject(url3, 
  new AsyncCallback<javascriptobject>() {
    public void onFailure(Throwable throwable) {
      GWT.log("got the JavaScriptObject");
      Window.alert("jsonp failed");
    }

    public void onSuccess(JavaScriptObject feed) {
      JSONObject obj = new JSONObject(feed);
      JSONValue val = obj.get("responseStatus");

      if(val != null)
      {
        JSONNumber num = val.isNumber();
        Window.alert("got the responseStatus " + num.doubleValue());  
      }
      else
      {
        Window.alert("not getting the responseData");
      }

    }
});