media: clarify MediaFormat.KEY_I_FRAME_INTERVAL

 * <tr><td>{@link #KEY_FRAME_RATE}</td><td>Integer or Float</td><td>required for <b>encoders</b>,

 *         optional for <b>decoders</b></td></tr>

 * <tr><td>{@link #KEY_CAPTURE_RATE}</td><td>Integer</td><td></td></tr>

 * <tr><td>{@link #KEY_I_FRAME_INTERVAL}</td><td>Integer</td><td><b>encoder-only</b></td></tr>

 * <tr><td>{@link #KEY_I_FRAME_INTERVAL}</td><td>Integer (or Float)</td><td><b>encoder-only</b>,

 *         time-interval between key frames.

 *         Float support added in {@link android.os.Build.VERSION_CODES#N_MR1}</td></tr>

 * <tr><td>{@link #KEY_INTRA_REFRESH_PERIOD}</td><td>Integer</td><td><b>encoder-only</b>, optional</td></tr>

 * <tr><td>{@link #KEY_MAX_WIDTH}</td><td>Integer</td><td><b>decoder-only</b>, optional, max-resolution width</td></tr>

 * <tr><td>{@link #KEY_MAX_HEIGHT}</td><td>Integer</td><td><b>decoder-only</b>, optional, max-resolution height</td></tr>

    public static final String KEY_CAPTURE_RATE = "capture-rate";

    /**

     * A key describing the frequency of I frames expressed in secs

     * between I frames.

     * The associated value is an integer.

     * A key describing the frequency of key frames expressed in seconds between key frames.

     * <p>

     * This key is used by video encoders.

     * A negative value means no key frames are requested after the first frame.

     * A zero value means a stream containing all key frames is requested.

     * <p class=note>

     * Most video encoders will convert this value of the number of non-key-frames between

     * key-frames, using the {@linkplain #KEY_FRAME_RATE frame rate} information; therefore,

     * if the actual frame rate differs (e.g. input frames are dropped or the frame rate

     * changes), the <strong>time interval</strong> between key frames will not be the

     * configured value.

     * <p>

     * The associated value is an integer (or float since

     * {@link android.os.Build.VERSION_CODES#N_MR1}).

     */

    public static final String KEY_I_FRAME_INTERVAL = "i-frame-interval";