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1、Android视频播放数据读取的流程http:/ Android4.0.1本地视频数据读取的流程，其他过程类似 当播放条件准备妥当之后，就要循环进行读取视频的原始数据放到MediaBuffer，将 MediaBuffer中的数据输送到解码器中解码，解码后的数据放到 MediaBuffer中，在将这 MediaBuffer中的数据进行 render显示。本文主要侧重读取原始数据的流程，主要是代码跟踪，不夹杂个人分析，有些mpeg4的算法不懂。1：onVideoEvent 中开始读取数据，具体代码如下：void AwesomePlayer:onVideoEvent() if (!mVideoBuf
2、fer) MediaSource:ReadOptions options;if (mSeeking != NO_SEEK) LOGV(seeking to %lld us (%.2f secs), mSeekTimeUs, mSeekTimeUs / 1E6);options.setSeekTo(mSeekTimeUs,mSeeking = SEEK_VIDEO_ONLY? MediaSource:ReadOptions:SEEK_NEXT_SYNC: MediaSource:ReadOptions:SEEK_CLOSEST_SYNC); for (;) status_t err = mVid
3、eoSource-read(&mVideoBuffer, 蓝色为核心代码，如果是正常读取，options 为 null，否则这个结构体中包含了 seek到的时间和 seek的模式，用于具体从文件中哪里开始读取，传入的mVideoBuffer引用用来装解码后的数据2：蓝色部分调用的是 OMXCodec:read函数，这个函数中核心的代码如下：status_t OMXCodec:read(MediaBuffer *buffer, const ReadOptions *options) status_t err = OK;*buffer = NULL;bool seeking = false;int
4、64_t seekTimeUs;ReadOptions:SeekMode seekMode;if (options & options-getSeekTo(&seekTimeUs, &seekMode) seeking = true;if (seeking) CODEC_LOGV(seeking to %lld us (%.2f secs), seekTimeUs, seekTimeUs / 1E6);CHECK(seekTimeUs = 0);mSeekTimeUs = seekTimeUs;mSeekMode = seekMode;drainInputBuffers();size_t in
5、dex = *mFilledBuffers.begin(); / A list of indices into mPortStatuskPortIndexOutput filled with data.mFilledBuffers.erase(mFilledBuffers.begin();BufferInfo *info = CHECK_EQ(int)info-mStatus, (int)OWNED_BY_US);info-mStatus = OWNED_BY_CLIENT;info-mMediaBuffer-add_ref();*buffer = info-mMediaBuffer;retu
6、rn OK;两点：a，drainInputBuffers 开始了数据的读取；b，mFilledBuffers 从这个队列中读取已经解码后的数据放入到传入的MediaBuffer中，mFilledBuffers 队列中的 MediaBuffer就是drainInputBuffers中写进去的3：跟到 drainInputBuffer中看看bool OMXCodec:drainInputBuffer(BufferInfo *info) CODEC_LOGV(calling emptyBuffer with codec specific data);status_t err = mOMX-empty
7、Buffer(mNode, info-mBuffer, 0, size,OMX_BUFFERFLAG_ENDOFFRAME | OMX_BUFFERFLAG_CODECCONFIG,0);CHECK_EQ(err, (status_t)OK);info-mStatus = OWNED_BY_COMPONENT;status_t err;bool signalEOS = false;int64_t timestampUs = 0;size_t offset = 0;int32_t n = 0;for (;) MediaBuffer *srcBuffer;if (mSeekTimeUs = 0)
8、MediaSource:ReadOptions options; options.setSeekTo(mSeekTimeUs, mSeekMode);mSeekTimeUs = -1;mSeekMode = ReadOptions:SEEK_CLOSEST_SYNC;err = mSource-read(if (err = OK) int64_t targetTimeUs;if (srcBuffer-meta_data()-findInt64(kKeyTargetTime, &targetTimeUs)& targetTimeUs = 0) CODEC_LOGV(targetTimeUs =
9、%lld us, targetTimeUs);mTargetTimeUs = targetTimeUs; else mTargetTimeUs = -1;CODEC_LOGV(Calling emptyBuffer on buffer %p (length %d), timestamp %lld us (%.2f secs),info-mBuffer, offset, timestampUs, timestampUs / 1E6);err = mOMX-emptyBuffer(mNode, info-mBuffer, 0, offset,flags, timestampUs);info-mSt
10、atus = OWNED_BY_COMPONENT;return true;两点：a，调用 err = mSource-read(从原始文件中读取原始数据，b，往 srcBuffer中读取数据前后，都调用 omx转移已经读取到该 info中的数据，目的是解码，解码后的数据就房子了 mFilledBuffers这个队列中；4：针对 mpeg4类型的视频，上面的 read函数调用的是 MPEG4Source的 read函数，核心代码如下：status_t MPEG4Source:read(MediaBuffer *out, const ReadOptions *options) *out = NU
11、LL;int64_t seekTimeUs;ReadOptions:SeekMode mode;if (options & options-getSeekTo(&seekTimeUs, &mode) if分支是用于有 seek的流程1：首先找到 seektime附近的 sampleIndex； 2：然后找到 sampleIndex附近的关键帧的 syncSampleIndex；3：然后 syncSampleIndex找到具体的 sampleTime，sampleTime 就是目前需要播放到的位置；4：mSampleTable-getMetaDataForSample 调用这个函数找到sampl
12、eTime时间的 offset和 size；5：有了 offset和 size之后剩下就是调用 mDataSource-readAt(offset, (uint8_t *)mBuffer-data(), size);读取数据放到 buffer中去了；uint32_t findFlags = 0;switch (mode) case ReadOptions:SEEK_PREVIOUS_SYNC:findFlags = SampleTable:kFlagBefore;break;case ReadOptions:SEEK_NEXT_SYNC:findFlags = SampleTable:kFla
13、gAfter;break;case ReadOptions:SEEK_CLOSEST_SYNC:case ReadOptions:SEEK_CLOSEST:findFlags = SampleTable:kFlagClosest;break;default:CHECK(!Should not be here.);break; uint32_t sampleIndex;status_t err = mSampleTable-findSampleAtTime(seekTimeUs * mTimescale / 1000000,uint32_t syncSampleIndex;if (err = O
14、K) err = mSampleTable-findSyncSampleNear(sampleIndex, uint32_t sampleTime;if (err = OK) err = mSampleTable-getMetaDataForSample(sampleIndex, NULL, NULL, if (mode = ReadOptions:SEEK_CLOSEST) targetSampleTimeUs = (sampleTime * 1000000ll) / mTimescale;mCurrentSampleIndex = syncSampleIndex; off64_t offs
15、et;size_t size;uint32_t cts;bool isSyncSample;bool newBuffer = false;if (mBuffer = NULL) newBuffer = true;status_t err =mSampleTable-getMetaDataForSample(mCurrentSampleIndex, &offset, &size, &cts, if (err != OK) return err;err = mGroup-acquire_buffer(if (err != OK) CHECK(mBuffer = NULL);return err; if (!mIsAVC | mWantsNALFragments) if (newBuffer) ssize_t num_bytes_read =mDataSource-readAt(offset, (uint8_t *)mBuffer-data(), size);CHECK(mBuffer != NULL);mBuffer-set_range(0, size);mBuffer-meta_data()-clear
