Android StagefrightPlayer调用流程

从Android 2.3开始，Android MediaPlayer采用Stagefright框架。Based on Android 4.0.1.

StagefrightPlayer创建函数如下：（MediaPlayerService.cpp，详细过程见文章:Android Audio 数据流详解）

 static sp<MediaPlayerBase> createPlayer(player_type playerType, void* cookie,
         notify_callback_f notifyFunc)
 {
     sp<MediaPlayerBase> p;
     switch (playerType) {
         case SONIVOX_PLAYER:
             LOGV(" create MidiFile");
             p = new MidiFile();
             break;
         case STAGEFRIGHT_PLAYER:
             LOGV(" create StagefrightPlayer");
             p = new StagefrightPlayer;
             break;
         case NU_PLAYER:
             LOGV(" create NuPlayer");
             p = new NuPlayerDriver;
             break;
         case TEST_PLAYER:
             LOGV("Create Test Player stub");
             p = new TestPlayerStub();
             break;
         default:
             LOGE("Unknown player type: %d", playerType);
             return NULL;
     }
     if (p != NULL) {
         if (p->initCheck() == NO_ERROR) {
             p->setNotifyCallback(cookie, notifyFunc);
         } else {
             p.clear();
         }
     }
     if (p == NULL) {
         LOGE("Failed to create player object");
     }
     return p;
 }

 static sp<MediaPlayerBase> createPlayer(player_type playerType, void* cookie,
         notify_callback_f notifyFunc)
 {
     sp<MediaPlayerBase> p;
     switch (playerType) {
         case SONIVOX_PLAYER:
             LOGV(" create MidiFile");
             p = new MidiFile();
             break;
         case STAGEFRIGHT_PLAYER:
             LOGV(" create StagefrightPlayer");
             p = new StagefrightPlayer;
             break;
         case NU_PLAYER:
             LOGV(" create NuPlayer");
             p = new NuPlayerDriver;
             break;
         case TEST_PLAYER:
             LOGV("Create Test Player stub");
             p = new TestPlayerStub();
             break;
         default:
             LOGE("Unknown player type: %d", playerType);
             return NULL;
     }
     if (p != NULL) {
         if (p->initCheck() == NO_ERROR) {
             p->setNotifyCallback(cookie, notifyFunc);
         } else {
             p.clear();
         }
     }
     if (p == NULL) {
         LOGE("Failed to create player object");
     }
     return p;
 }

首先了解下系统本身的调用流程，StagefrightPlayer使用的AwesomePlayer来实现的，首先是Demuxer的实现，对于系统本身不支持的格式是没有分离器的，具体查看代码（本文以本地文件播放为例）.

1. Demuxer的实现
Awesomeplayer.cpp的setDataSource_l(
  const sp<DataSource> &dataSource) {
  sp<MediaExtractor> extractor = MediaExtractor::Create(dataSource);

这个就是创建Demux的地方，查看代码MediaExtractor.cpp的create函数，datasource的sniff函数就是自动检测媒体格式容器的类型的，如果需要新增原系统无法识别的媒体格式，必然无法得到有效的分离器，所以这里需要自己创建自己Demuxer，每一种格式的XXXXExtractor.cpp函数中有个SniffXXXX函数，在Awesomeplayer的构造函数中的这一句DataSource::RegisterDefaultSniffers()就是注册好所有的sniff函数，写一个自己的XXXExtractor类，照样写个XXXXsinff函数，在RegisterDefaultSniffers中加入自己的函数。然后自已实现一个需要的Demuxer.通过Demuxer分离出音视频流后，就是进入解码阶段了。

 

2. AV Decoder

status_t AwesomePlayer::initVideoDecoder() {
  mVideoSource = OMXCodec::Create(
  mClient.interface(), mVideoTrack->getFormat(),
  false,  
  mVideoTrack);
这个就是创建的解码器了，create的最后一个参数就是分离出来的独立的视频流，具备的接口最重要的就是read接口，是分离器中实现的，这个track是XXXXExtractor中的getTrack获取的。

解码器的逻辑主要集中在OMXCodec.cpp中，在OMXCodec::Create中主要负责寻找匹配的codec并创建codec.

寻找匹配的codec:

 Vector<String8> matchingCodecs;
 findMatchingCodecs(
         mime, createEncoder, matchComponentName, flags, &matchingCodecs);

 if (matchingCodecs.isEmpty()) {
     return NULL;
 }

 Vector<String8> matchingCodecs;
 findMatchingCodecs(
         mime, createEncoder, matchComponentName, flags, &matchingCodecs);

 if (matchingCodecs.isEmpty()) {
     return NULL;
 }

创建codec:

 status_t err = omx->allocateNode(componentName, observer, &node);
 if (err == OK) {
     LOGV("Successfully allocated OMX node '%s'", componentName);

     sp<OMXCodec> codec = new OMXCodec(
             omx, node, quirks, flags,
             createEncoder, mime, componentName,
             source, nativeWindow);

     observer->setCodec(codec);

     err = codec->configureCodec(meta);

     if (err == OK) {
         if (!strcmp("OMX.Nvidia.mpeg2v.decode", componentName)) {
             codec->mFlags |= kOnlySubmitOneInputBufferAtOneTime;
         }

         return codec;
     }

     LOGV("Failed to configure codec '%s'", componentName);
 }

 status_t err = omx->allocateNode(componentName, observer, &node);
 if (err == OK) {
     LOGV("Successfully allocated OMX node '%s'", componentName);

     sp<OMXCodec> codec = new OMXCodec(
             omx, node, quirks, flags,
             createEncoder, mime, componentName,
             source, nativeWindow);

     observer->setCodec(codec);

     err = codec->configureCodec(meta);

     if (err == OK) {
         if (!strcmp("OMX.Nvidia.mpeg2v.decode", componentName)) {
             codec->mFlags |= kOnlySubmitOneInputBufferAtOneTime;
         }

         return codec;
     }

     LOGV("Failed to configure codec '%s'", componentName);
 }

findMatchingCodecs这个函数就是查找解码器的，它在kDecoderInfo数组中寻找需要的解码器。

 

 void OMXCodec::findMatchingCodecs(
         const char *mime,
         bool createEncoder, const char *matchComponentName,
         uint32_t flags,
         Vector<String8> *matchingCodecs) {
     matchingCodecs->clear();

     for (int index = 0;; ++index) {
         const char *componentName;

         if (createEncoder) {
             componentName = GetCodec(
                     kEncoderInfo,
                     sizeof(kEncoderInfo) / sizeof(kEncoderInfo[0]),
                     mime, index);
         } else {
             componentName = GetCodec(
                     kDecoderInfo,
                     sizeof(kDecoderInfo) / sizeof(kDecoderInfo[0]),
                     mime, index);
         }

         if (!componentName) {
             break;
         }

         // If a specific codec is requested, skip the non-matching ones.
         if (matchComponentName && strcmp(componentName, matchComponentName)) {
             continue;
         }

         // When requesting software-only codecs, only push software codecs
         // When requesting hardware-only codecs, only push hardware codecs
         // When there is request neither for software-only nor for
         // hardware-only codecs, push all codecs
         if (((flags & kSoftwareCodecsOnly) &&   IsSoftwareCodec(componentName)) ||
             ((flags & kHardwareCodecsOnly) &&  !IsSoftwareCodec(componentName)) ||
             (!(flags & (kSoftwareCodecsOnly | kHardwareCodecsOnly)))) {

             matchingCodecs->push(String8(componentName));
         }
     }

     if (flags & kPreferSoftwareCodecs) {
         matchingCodecs->sort(CompareSoftwareCodecsFirst);
     }
 }

 void OMXCodec::findMatchingCodecs(
         const char *mime,
         bool createEncoder, const char *matchComponentName,
         uint32_t flags,
         Vector<String8> *matchingCodecs) {
     matchingCodecs->clear();

     for (int index = 0;; ++index) {
         const char *componentName;

         if (createEncoder) {
             componentName = GetCodec(
                     kEncoderInfo,
                     sizeof(kEncoderInfo) / sizeof(kEncoderInfo[0]),
                     mime, index);
         } else {
             componentName = GetCodec(
                     kDecoderInfo,
                     sizeof(kDecoderInfo) / sizeof(kDecoderInfo[0]),
                     mime, index);
         }

         if (!componentName) {
             break;
         }

         // If a specific codec is requested, skip the non-matching ones.
         if (matchComponentName && strcmp(componentName, matchComponentName)) {
             continue;
         }

         // When requesting software-only codecs, only push software codecs
         // When requesting hardware-only codecs, only push hardware codecs
         // When there is request neither for software-only nor for
         // hardware-only codecs, push all codecs
         if (((flags & kSoftwareCodecsOnly) &&   IsSoftwareCodec(componentName)) ||
             ((flags & kHardwareCodecsOnly) &&  !IsSoftwareCodec(componentName)) ||
             (!(flags & (kSoftwareCodecsOnly | kHardwareCodecsOnly)))) {

             matchingCodecs->push(String8(componentName));
         }
     }

     if (flags & kPreferSoftwareCodecs) {
         matchingCodecs->sort(CompareSoftwareCodecsFirst);
     }
 }

差不多流程是这样把，关于显示部分就不用管了，解码器对接render部分，应该自己会弄好，解码器最重要的对外接口也就是read接口的，返回的一帧帧的解码后的数据。