Android O MediaCodecList 分析

//static
void MediaCodecList::findMatchingCodecs(
        const char *mime, bool encoder, uint32_t flags,
        Vector *matches, Vector *owners) {
    matches->clear();
    if (owners != nullptr) {
        owners->clear();
    }

    const sp list = getInstance();
    if (list == nullptr) {
        return;
    }

    size_t index = 0;
    for (;;) {
        ssize_t matchIndex =
            list->findCodecByType(mime, encoder, index);

        if (matchIndex < 0) {
            break;
        }

        index = matchIndex + 1;

        const sp info = list->getCodecInfo(matchIndex);
        CHECK(info != nullptr);
        AString componentName = info->getCodecName();

        if ((flags & kHardwareCodecsOnly) && isSoftwareCodec(componentName)) {
            ALOGV("skipping SW codec '%s'", componentName.c_str());
        } else {
            matches->push(componentName);
            if (owners != nullptr) {
                owners->push(AString(info->getOwnerName()));
            }
            ALOGV("matching '%s'", componentName.c_str());
        }
    }

    if (flags & kPreferSoftwareCodecs ||
            property_get_bool("debug.stagefright.swcodec", false)) {
        matches->sort(compareSoftwareCodecsFirst);
    }
}

 如上截图： 核心方法findMatchingCodecs

                    可以过滤软编码：

                    if ((flags & kHardwareCodecsOnly) && isSoftwareCodec(componentName)) {

                    }else{

                     . . .  

                   }

 在MediaCodecSource.cpp 以及 ACodec.cpp 都会调用findMatchingCodecs

status_t MediaCodecSource::initEncoder() {
    mReflector = new AHandlerReflector(this);
    mLooper->registerHandler(mReflector);

    mCodecLooper = new ALooper;
    mCodecLooper->setName("codec_looper");
    mCodecLooper->start();

    if (mFlags & FLAG_USE_SURFACE_INPUT) {
        mOutputFormat->setInt32("create-input-buffers-suspended", 1);
    }

    AString outputMIME;
    CHECK(mOutputFormat->findString("mime", &outputMIME));

    Vector matchingCodecs;
    ALOGD("-[TIM]- mFlags & FLAG_PREFER_SOFTWARE_CODEC:%d, MiME-NAME:%s .", mFlags & FLAG_PREFER_SOFTWARE_CODEC,outputMIME.c_str());
    MediaCodecList::findMatchingCodecs(
            outputMIME.c_str(),
            true, /* encoder */
           ((mFlags & FLAG_PREFER_SOFTWARE_CODEC) ? MediaCodecList::kPreferSoftwareCodecs : 0),//
            &matchingCodecs);

 

bool ACodec::UninitializedState::onAllocateComponent(const sp &msg) {
    ALOGV("onAllocateComponent");

    CHECK(mCodec->mOMXNode == NULL);

    sp notify = new AMessage(kWhatOMXDied, mCodec);

    Vector matchingCodecs;
    Vector owners;

    AString mime;

    AString componentName;
    int32_t encoder = false;
    if (msg->findString("componentName", &componentName)) {
         . . . 
    } else {
    ALOGW("-[TIM]-findString componentName is null");
        CHECK(msg->findString("mime", &mime));

        if (!msg->findInt32("encoder", &encoder)) {
            encoder = false;
        }

        MediaCodecList::findMatchingCodecs(
                mime.c_str(),
                encoder, // createEncoder
                0,       // flags
                &matchingCodecs,
                &owners);
    }