对于http streaming，更新buffer进度的处理在AwesomePlayer::onBufferingUpdate()函数中，首先判断mCachedSource != NULL，即是http://流媒体的情况下，通过getBitrate(&bitrate)函数取得bitrate，然后计算出buffer的进度，通过notifyListener_l(MEDIA_BUFFERING_UPDATE, percentage)发消息，在MediaPlayer.cpp类对应MediaPlayer::notify函数接收到MEDIA_BUFFERING_UPDATE消息，然后在应用层通过注册MediaPlayer的setOnBufferingUpdateListener监听，接收到MEDIA_BUFFERING_UPDATE消息，即可以获得buffer更新的进度值percent。
1.AwesomePlayer::onBufferingUpdate()函数
计算buffer更新的percent
- if (getBitrate(&bitrate)) {
- LOGV("onBufferingUpdate: bitrate: %lld", bitrate);
- size_t lowWaterThreshold = (size_t) ((bitrate * kLowWaterMarkUs
- * (1.0f + kThresholdPaddingFactor)) / 8000000ll);
- size_t highWaterThreshold = (size_t) ((bitrate
- * kHighWaterMarkUs * (1.0f + kThresholdPaddingFactor))
- / 8000000ll);
- mCachedSource->setThresholds(lowWaterThreshold,
- highWaterThreshold);
- size_t cachedSize = mCachedSource->cachedSize();
- int64_t cachedDurationUs = cachedSize * 8000000ll / bitrate;
- int percentage = 100.0 * (double)cachedDurationUs / mDurationUs;
- if (percentage > 100) {
- percentage = 100;
- }
- notifyListener_l(MEDIA_BUFFERING_UPDATE, percentage);
- } else {
其中8000000ll为1byte以us为单位的bit数，单位long long类型，即1byte = 1byte * 8bits/byte * 1000000us = 8000000ll
2.AwesomePlayer::getBitrate函数
- bool AwesomePlayer::getBitrate(int64_t *bitrate) {
- off64_t size;
- if (mDurationUs >= 0 && mCachedSource != NULL
- && mCachedSource->getSize(&size) == OK) {
- *bitrate = size * 8000000ll / mDurationUs; // in bits/sec
- return true;
- }
- if (mBitrate >= 0) {
- *bitrate = mBitrate;
- return true;
- }
- *bitrate = 0;
- return false;
- }
3. NuCachedSource2::getSize
调用其成员变量mSource的getSize函数取得当前更新的size大小，mSouce即为NuCachedSource2构造函数传递的参数，此参数为AwesomePlayer::finishSetDataSource_l()函数中创建mCachedSource对象时传递的类型为NuHTTPDataSource的参数mConnectingDataSource。
所以，mSource->getSize调用的是NuHTTPDataSource的getSize函数。
- status_t NuCachedSource2::getSize(off64_t *size) {
- return mSource->getSize(size);
- }
4.NuHTTPDataSource::getSize函数
此函数取得size值为mContentLength的值，取得mContentLength的值的处理在NuHTTPDataSource::connect函数，从http header中读取的，即从"Content-Length"或者"Content-Range"头域指定的值中计算出的。
NuCachedSource2和NuHTTPDataSource类以及getSize函数的关系图如下：
5.mediaplayer.cpp的MediaPlayer::notify函数
- void MediaPlayer::notify(int msg, int ext1, int ext2)
- {
- ...
- case MEDIA_BUFFERING_UPDATE:
- LOGV("buffering %d", ext1);
- break;
- ...
- sp<MediaPlayerListener> listener = mListener;
- if (locked) mLock.unlock();
- // this prevents re-entrant calls into client code
- if ((listener != 0) && send) {
- Mutex::Autolock _l(mNotifyLock);
- LOGV("callback application");
- listener->notify(msg, ext1, ext2); // 发送消息给MediaPlayer.java，然后应用层就接收到
- LOGV("back from callback");
- }
6.MediaPlayer.java的setOnBufferingUpdateListener函数
在onBufferingUpdate函数中的参数percent即为buffer更新进度值0-100.
- /**
- * Interface definition of a callback to be invoked indicating buffering
- * status of a media resource being streamed over the network.
- */
- public interface OnBufferingUpdateListener
- {
- /**
- * Called to update status in buffering a media stream.
- *
- * @param mp the MediaPlayer the update pertains to
- * @param percent the percentage (0-100) of the buffer
- * that has been filled thus far
- */
- void onBufferingUpdate(MediaPlayer mp, int percent);
- }
- /**
- * Register a callback to be invoked when the status of a network
- * stream's buffer has changed.
- *
- * @param listener the callback that will be run.
- */
- public void setOnBufferingUpdateListener(OnBufferingUpdateListener listener)
- {
- mOnBufferingUpdateListener = listener;
- }