Android MediaPlayer SeekTo 在 8.0 版本上最佳化說明

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android使用 mediaPlayer 播放video視頻過程中, 當使用者退出當前播放，再從後台恢複播放時，需要跳轉到之前退出的時間點繼續播放。使用的方法基本都是 SeekTo 之前的時間點，但是經常遇到恢複播放時位置不準的問題，而且甚至有重頭開始播放的現象。這個是因為SeekTo是回到上一時間點附近的主要畫面格導致的。

針對這個問題，在最新的android 8.0平台上，已經有了新的解決方案：

SeekTo() 方法在android O 平台新增了一個多參數的方法：

void seekTo（long msec, @SeekMode int mode）

這裡的Mode 傳入

int SEEK_CLOSEST = 0x03 

就不會出現播放視頻位置不準確的現象了。

/**     * Seek modes used in method seekTo(long, int) to move media position     * to a specified location.     *     * Do not change these mode values without updating their counterparts     * in include/media/IMediaSource.h!     */    /**     * This mode is used with {@link #seekTo(long, int)} to move media position to     * a sync (or key) frame associated with a data source that is located     * right before or at the given time.     *     * @see #seekTo(long, int)     */    public static final int SEEK_PREVIOUS_SYNC    = 0x00;    /**     * This mode is used with {@link #seekTo(long, int)} to move media position to     * a sync (or key) frame associated with a data source that is located     * right after or at the given time.     *     * @see #seekTo(long, int)     */    public static final int SEEK_NEXT_SYNC        = 0x01;    /**     * This mode is used with {@link #seekTo(long, int)} to move media position to     * a sync (or key) frame associated with a data source that is located     * closest to (in time) or at the given time.     *     * @see #seekTo(long, int)     */    public static final int SEEK_CLOSEST_SYNC     = 0x02;    /**     * This mode is used with {@link #seekTo(long, int)} to move media position to     * a frame (not necessarily a key frame) associated with a data source that     * is located closest to or at the given time.     *     * @see #seekTo(long, int)     */    public static final int SEEK_CLOSEST          = 0x03;    /** @hide */    @IntDef(        value = {            SEEK_PREVIOUS_SYNC,            SEEK_NEXT_SYNC,            SEEK_CLOSEST_SYNC,            SEEK_CLOSEST,    })    @Retention(RetentionPolicy.SOURCE)    public @interface SeekMode {}    private native final void _seekTo(long msec, int mode);    /**     * Moves the media to specified time position by considering the given mode.     * <p>     * When seekTo is finished, the user will be notified via OnSeekComplete supplied by the user.     * There is at most one active seekTo processed at any time. If there is a to-be-completed     * seekTo, new seekTo requests will be queued in such a way that only the last request     * is kept. When current seekTo is completed, the queued request will be processed if     * that request is different from just-finished seekTo operation, i.e., the requested     * position or mode is different.     *     * @param msec the offset in milliseconds from the start to seek to.     * When seeking to the given time position, there is no guarantee that the data source     * has a frame located at the position. When this happens, a frame nearby will be rendered.     * If msec is negative, time position zero will be used.     * If msec is larger than duration, duration will be used.     * @param mode the mode indicating where exactly to seek to.     * Use {@link #SEEK_PREVIOUS_SYNC} if one wants to seek to a sync frame     * that has a timestamp earlier than or the same as msec. Use     * {@link #SEEK_NEXT_SYNC} if one wants to seek to a sync frame     * that has a timestamp later than or the same as msec. Use     * {@link #SEEK_CLOSEST_SYNC} if one wants to seek to a sync frame     * that has a timestamp closest to or the same as msec. Use     * {@link #SEEK_CLOSEST} if one wants to seek to a frame that may     * or may not be a sync frame but is closest to or the same as msec.     * {@link #SEEK_CLOSEST} often has larger performance overhead compared     * to the other options if there is no sync frame located at msec.     * @throws IllegalStateException if the internal player engine has not been     * initialized     * @throws IllegalArgumentException if the mode is invalid.     */    public void seekTo(long msec, @SeekMode int mode) {        if (mode < SEEK_PREVIOUS_SYNC || mode > SEEK_CLOSEST) {            final String msg = "Illegal seek mode: " + mode;            throw new IllegalArgumentException(msg);        }        // TODO: pass long to native, instead of truncating here.        if (msec > Integer.MAX_VALUE) {            Log.w(TAG, "seekTo offset " + msec + " is too large, cap to " + Integer.MAX_VALUE);            msec = Integer.MAX_VALUE;        } else if (msec < Integer.MIN_VALUE) {            Log.w(TAG, "seekTo offset " + msec + " is too small, cap to " + Integer.MIN_VALUE);            msec = Integer.MIN_VALUE;        }        _seekTo(msec, mode);    }

Android MediaPlayer SeekTo 在 8.0 版本上最佳化說明