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Commit 03a4090b authored by Eric Laurent's avatar Eric Laurent
Browse files

Update java doc for visualizer FFT capture. 

The java doc for visualizer FFT capture was not describing
correctly the layout of the data returned by getFft() method.

Change-Id: Idec09538490ea73b211db253b1b8b733ca4d4a72
parent 7d452f69

media/java/android/media/audiofx/Visualizer.java

+38 −8
Original line number Diff line number Diff line
@@ -43,10 +43,8 @@ import android.os.Message; 
 *   <li>Frequency data: 8-bit magnitude FFT by using the {@link #getFft(byte[])} method</li>

 * </ul>

 * <p>The length of the capture can be retrieved or specified by calling respectively

 * {@link #getCaptureSize()} and {@link #setCaptureSize(int)} methods. Note that the size of the FFT

 * is half of the specified capture size but both sides of the spectrum are returned yielding in a

 * number of bytes equal to the capture size. The capture size must be a power of 2 in the range

 * returned by {@link #getCaptureSizeRange()}.

 * {@link #getCaptureSize()} and {@link #setCaptureSize(int)} methods. The capture size must be a

 * power of 2 in the range returned by {@link #getCaptureSizeRange()}.

 * <p>In addition to the polling capture mode described above with {@link #getWaveForm(byte[])} and

 *  {@link #getFft(byte[])} methods, a callback mode is also available by installing a listener by

 *  use of the {@link #setDataCaptureListener(OnDataCaptureListener, int, boolean, boolean)} method.
@@ -333,11 +331,43 @@ public class Visualizer { 
        }

    }

    /**

     * Returns a frequency capture of currently playing audio content. The capture is a 8-bit

     * magnitude FFT. Note that the size of the FFT is half of the specified capture size but both

     * sides of the spectrum are returned yielding in a number of bytes equal to the capture size.

     * {@see #getCaptureSize()}.

     * Returns a frequency capture of currently playing audio content.

     * <p>This method must be called when the Visualizer is enabled.

     * <p>The capture is an 8-bit magnitude FFT, the frequency range covered being 0 (DC) to half of

     * the sampling rate returned by {@link #getSamplingRate()}. The capture returns the real and

     * imaginary parts of a number of frequency points equal to half of the capture size plus one.

     * <p>Note: only the real part is returned for the first point (DC) and the last point

     * (sampling frequency / 2).

     * <p>The layout in the returned byte array is as follows:

     * <ul>

     *   <li> n is the capture size returned by getCaptureSize()</li>

     *   <li> Rfk, Ifk are respectively  the real and imaginary parts of the kth frequency

     *   component</li>

     *   <li> If Fs is the sampling frequency retuned by getSamplingRate() the kth frequency is:

     *   (k*Fs)/(n/2) </li>

     * </ul>

     * <table border="0" cellspacing="0" cellpadding="0">

     * <tr><td>Index </p></td>

     *     <td>0 </p></td>

     *     <td>1 </p></td>

     *     <td>2 </p></td>

     *     <td>3 </p></td>

     *     <td>4 </p></td>

     *     <td>5 </p></td>

     *     <td>... </p></td>

     *     <td>n - 2 </p></td>

     *     <td>n - 1 </p></td></tr>

     * <tr><td>Data </p></td>

     *     <td>Rf0 </p></td>

     *     <td>Rf(n/2) </p></td>

     *     <td>Rf1 </p></td>

     *     <td>If1 </p></td>

     *     <td>Rf2 </p></td>

     *     <td>If2 </p></td>

     *     <td>... </p></td>

     *     <td>Rf(n-1)/2 </p></td>

     *     <td>If(n-1)/2 </p></td></tr>

     * </table>

     * @param fft array of bytes where the FFT should be returned

     * @return {@link #SUCCESS} in case of success,

     * {@link #ERROR_NO_MEMORY}, {@link #ERROR_INVALID_OPERATION} or {@link #ERROR_DEAD_OBJECT}