Android MediaExtractor setDataSource
0. setDataSource时序图
1. MediaExtractor(java)
file: frameworks/base/media/java/android/mediaf/MediaExtractor.java
目前Android 5.0仅支持本地视频
public final void setDataSource(FileDescriptor fd) throws IOException {
setDataSource(fd, 0, 0x7ffffffffffffffL);
}这会调用JNI setDataSource
2. android_media_MediaExtractor(native)
file: frameworks/base/media/jni/android_media_MediaExtractor.cpp
native的setDataSource是调用NuMediaExtractor的setDataSource
status_t JMediaExtractor::setDataSource(int fd, off64_t offset, off64_t size) {
return mImpl->setDataSource(fd, offset, size);
}3. NuMediaExtractor
file：frameworks/av/media/libstagefright/NuMediaExtractor.cpp
NuMediaExtractor先创建FileSource
然后根据FileSource创建相应的Extractor
status_t NuMediaExtractor::setDataSource(int fd, off64_t offset, off64_t size) {
...
sp<FileSource> fileSource = new FileSource(dup(fd), offset, size);
mImpl = MediaExtractor::Create(fileSource);
...
mDataSource = fileSource;
updateDurationAndBitrate();
return OK;
}4. New FileSource
FileSource继承于DataSource。
FileSource初始化函数执行操作有：打开文件，获取文件FD，Seek文件
FileSource::FileSource(const char *filename)
: mFd(-1),
mOffset(0),
mLength(-1),
mDecryptHandle(NULL),
mDrmManagerClient(NULL),
mDrmBufOffset(0),
mDrmBufSize(0),
mDrmBuf(NULL){
mFd = open(filename, O_LARGEFILE | O_RDONLY);
if (mFd >= 0) {
mLength = lseek64(mFd, 0, SEEK_END);
} else {
ALOGE("Failed to open file '%s'. (%s)", filename, strerror(errno));
}
}DataSource初始化函数执行操作有：new Sniffer
DataSource() : mSniffer(new Sniffer()) {}Sniffer构造过程：注册各个Extractor的Sniffer函数
registerDefaultSniffers
void Sniffer::registerDefaultSniffers() {
Mutex::Autolock autoLock(mSnifferMutex);
registerSniffer_l(SniffMPEG4);
registerSniffer_l(SniffMatroska);
registerSniffer_l(SniffOgg);
registerSniffer_l(SniffWAV);
registerSniffer_l(SniffFLAC);
registerSniffer_l(SniffAMR);
registerSniffer_l(SniffMPEG2TS);
registerSniffer_l(SniffMP3);
registerSniffer_l(SniffAAC);
registerSniffer_l(SniffMPEG2PS);
registerSniffer_l(SniffWVM);
registerSniffer_l(ExtendedExtractor::Sniff);
char value[PROPERTY_VALUE_MAX];
if (property_get("drm.service.enabled", value, NULL)
&& (!strcmp(value, "1") || !strcasecmp(value, "true"))) {
registerSniffer_l(SniffDRM);
}
}5. MediaExtractor::Create
file:frameworks/av/media/libstagefright/MediaExtractor.cpp
MediaExtractor（C++）是MediaExtractor体系中核心，是各个extractor（eg.MPEG4Extractor）的父类，管理者.
Create它根据文件的MIME信息创建对应的Extractor，具体逻辑如下：
（1）sniff ： 获取文件meta信息
（2）根据meta中的MIME创建对应的Extractor
（3）ExtendedUtils判断创建默认Extractor还是扩展Extractor
sp<MediaExtractor> MediaExtractor::Create(
const sp<DataSource> &source, const char *mime) {
sp<AMessage> meta;
String8 tmp;
if (mime == NULL) {
float confidence;
if (!source->sniff(&tmp, &confidence, &meta)) {
ALOGV("FAILED to autodetect media content.");
return NULL;
}
mime = tmp.string();
ALOGV("Autodetected media content as '%s' with confidence %.2f",
mime, confidence);
}
bool isDrm = false;
// DRM MIME type syntax is "drm+type+original" where
// type is "es_based" or "container_based" and
// original is the content's cleartext MIME type
if (!strncmp(mime, "drm+", 4)) {
const char *originalMime = strchr(mime+4, '+');
if (originalMime == NULL) {
// second + not found
return NULL;
}
++originalMime;
if (!strncmp(mime, "drm+es_based+", 13)) {
// DRMExtractor sets container metadata kKeyIsDRM to 1
return new DRMExtractor(source, originalMime);
} else if (!strncmp(mime, "drm+container_based+", 20)) {
mime = originalMime;
isDrm = true;
} else {
return NULL;
}
}
MediaExtractor *ret = NULL;
if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG4)
|| !strcasecmp(mime, "audio/mp4")) {
ret = new MPEG4Extractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_MPEG)) {
ret = new MP3Extractor(source, meta);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AMR_NB)
|| !strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AMR_WB)) {
ret = new AMRExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_FLAC)) {
ret = new FLACExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WAV)) {
ret = new WAVExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_OGG)) {
ret = new OggExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MATROSKA)) {
ret = new MatroskaExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG2TS)) {
ret = new MPEG2TSExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WVM)) {
// Return now. WVExtractor should not have the DrmFlag set in the block below.
return new WVMExtractor(source);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AAC_ADTS)) {
ret = new AACExtractor(source, meta);
} else if (!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG2PS)) {
ret = new MPEG2PSExtractor(source);
}
if (ret != NULL) {
if (isDrm) {
ret->setDrmFlag(true);
} else {
ret->setDrmFlag(false);
}
}
return ExtendedUtils::MediaExtractor_CreateIfNeeded(ret, source, mime);
}6. ExtendedUtils::MediaExtractor_CreateIfNeeded
MediaExtractor_CreateIfNeeded的作用如其名就是判断是否需要启用ExtentedExtractor。
如果看源代码的话会发现整个过程比较繁琐，下面说下启用ExtentedExtractor的原则，（如果需要深究还是仔细阅读源代码好了），原则如下：
（1）尽量采用ExtentedExtractor
因为DefaultExtractor是google的decoder，采用的是软解；ExtentedExtractor一般是厂商的decoder，通常采用硬解。
（2）如果无法正确获取多媒体信息则采用ExtentedExtractor
（3）如果没有找到DefaultExtractor则采用ExtentedExtractor
（4）对于某些特殊格式采用ExtentedExtractor
比如MPEG4格式，这个一般厂商都支持硬解。
sp<MediaExtractor> ExtendedUtils::MediaExtractor_CreateIfNeeded(sp<MediaExtractor> defaultExt,
const sp<DataSource> &source,
const char *mime) {
bool bCheckExtendedExtractor = false;
bool videoTrackFound = false;
bool audioTrackFound = false;
bool amrwbAudio = false;
bool hevcVideo = false;
bool dolbyAudio = false;
bool mpeg4Container = false;
bool aacAudioTrack = false;
int numOfTrack = 0;
mpeg4Container = !strncasecmp(mime,
MEDIA_MIMETYPE_CONTAINER_MPEG4,
strlen(MEDIA_MIMETYPE_CONTAINER_MPEG4));
if (defaultExt != NULL) {
for (size_t trackItt = 0; trackItt < defaultExt->countTracks(); ++trackItt) {
++numOfTrack;
sp<MetaData> meta = defaultExt->getTrackMetaData(trackItt);
const char *_mime;
CHECK(meta->findCString(kKeyMIMEType, &_mime));
String8 mime = String8(_mime);
const char * dolbyFormats[ ] = {
MEDIA_MIMETYPE_AUDIO_AC3,
MEDIA_MIMETYPE_AUDIO_EAC3,
#ifdef DOLBY_UDC
MEDIA_MIMETYPE_AUDIO_EAC3_JOC,
#endif
};
if (!strncasecmp(mime.string(), "audio/", 6)) {
audioTrackFound = true;
amrwbAudio = !strncasecmp(mime.string(),
MEDIA_MIMETYPE_AUDIO_AMR_WB,
strlen(MEDIA_MIMETYPE_AUDIO_AMR_WB));
aacAudioTrack = !strncasecmp(mime.string(),
MEDIA_MIMETYPE_AUDIO_AAC,
strlen(MEDIA_MIMETYPE_AUDIO_AAC));
for (size_t i = 0; i < ARRAY_SIZE(dolbyFormats); i++) {
if (!strncasecmp(mime.string(), dolbyFormats[i], strlen(dolbyFormats[i]))) {
dolbyAudio = true;
}
}
if (amrwbAudio || dolbyAudio) {
break;
}
} else if (!strncasecmp(mime.string(), "video/", 6)) {
videoTrackFound = true;
if(!strncasecmp(mime.string(), "video/hevc", 10)) {
hevcVideo = true;
}
}
}
if (amrwbAudio || dolbyAudio) {
bCheckExtendedExtractor = true;
} else if (numOfTrack == 0) {
bCheckExtendedExtractor = true;
} else if (numOfTrack == 1) {
if ((videoTrackFound) ||
(!videoTrackFound && !audioTrackFound) ||
(audioTrackFound && mpeg4Container && aacAudioTrack)) {
bCheckExtendedExtractor = true;
}
} else if (numOfTrack >= 2) {
if (videoTrackFound && audioTrackFound) {
if (amrwbAudio || hevcVideo ) {
bCheckExtendedExtractor = true;
}
} else {
bCheckExtendedExtractor = true;
}
}
} else {
bCheckExtendedExtractor = true;
}
if (!bCheckExtendedExtractor) {
ALOGD("extended extractor not needed, return default");
return defaultExt;
}
//Create Extended Extractor only if default extractor is not selected
ALOGD("Try creating ExtendedExtractor");
sp<MediaExtractor> retExtExtractor = ExtendedExtractor::Create(source, mime);
if (retExtExtractor == NULL) {
ALOGD("Couldn't create the extended extractor, return default one");
return defaultExt;
}
if (defaultExt == NULL) {
ALOGD("default extractor is NULL, return extended extractor");
return retExtExtractor;
}
//bCheckExtendedExtractor is true which means default extractor was found
//but we want to give preference to extended extractor based on certain
//conditions.
//needed to prevent a leak in case both extractors are valid
//but we still dont want to use the extended one. we need
//to delete the new one
bool bUseDefaultExtractor = true;
const char * extFormats[ ] = {
MEDIA_MIMETYPE_AUDIO_AMR_WB_PLUS,
MEDIA_MIMETYPE_VIDEO_HEVC,
MEDIA_MIMETYPE_AUDIO_AC3,
MEDIA_MIMETYPE_AUDIO_EAC3,
#ifdef DOLBY_UDC
MEDIA_MIMETYPE_AUDIO_EAC3_JOC,
#endif
MEDIA_MIMETYPE_AUDIO_AAC,
};
for (size_t trackItt = 0; (trackItt < retExtExtractor->countTracks()); ++trackItt) {
sp<MetaData> meta = retExtExtractor->getTrackMetaData(trackItt);
const char *mime;
bool success = meta->findCString(kKeyMIMEType, &mime);
bool isExtFormat = false;
for (size_t i = 0; i < ARRAY_SIZE(extFormats); i++) {
if (!strncasecmp(mime, extFormats[i], strlen(extFormats[i]))) {
isExtFormat = true;
break;
}
}
if ((success == true) && isExtFormat) {
ALOGD("Discarding default extractor and using the extended one");
bUseDefaultExtractor = false;
break;
}
}
if (bUseDefaultExtractor) {
ALOGD("using default extractor inspite of having a new extractor");
retExtExtractor.clear();
return defaultExt;
} else {
defaultExt.clear();
return retExtExtractor;
}
}