stagefright的codec—1

 

多媒體檔案經過解析後，需要根據mime尋找適合的codec，2.3的系統有兩種方式 SoftwareCodec和omx的node codec，後者可以結合特殊硬體做最佳化處理，前者感覺就是比較標準的軟解碼。

下面是代碼

omxcodec.cpp

omxcodec::create

Vector<String8> matchingCodecs;------系統對於某種mime的所有codec集合
    findMatchingCodecs(
            mime, createEncoder, matchComponentName, flags, &matchingCodecs);

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

    sp<OMXCodecObserver> observer = new OMXCodecObserver;
    IOMX::node_id node = 0;

    const char *componentName;
    for (size_t i = 0; i < matchingCodecs.size(); ++i) {--------去其中遍曆所有的codec，一般是omx的node先，然後是軟解碼
        componentName = matchingCodecs[i].string();

        sp<MediaSource> softwareCodec = createEncoder?
            InstantiateSoftwareEncoder(componentName, source, meta):
            InstantiateSoftwareCodec(componentName, source);

        if (softwareCodec != NULL) {
            LOGV("Successfully allocated software codec '%s'", componentName);

            return softwareCodec;-----------------是軟解碼-返回codec
        }

        LOGV("Attempting to allocate OMX node '%s'", componentName);

        uint32_t quirks = getComponentQuirks(componentName, createEncoder);

        if (!createEncoder
                && (quirks & kOutputBuffersAreUnreadable)
                && (flags & kClientNeedsFramebuffer)) {
            if (strncmp(componentName, "OMX.SEC.", 8)) {
                // For OMX.SEC.* decoders we can enable a special mode that
                // gives the client access to the framebuffer contents.

                LOGW("Component '%s' does not give the client access to "
                     "the framebuffer contents. Skipping.",
                     componentName);

                continue;
            }
        }

        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,
                    createEncoder, mime, componentName,
                    source);------------------------產生一個omxcodec，這個需要後面再細細研究

            observer->setCodec(codec);

            err = codec->configureCodec(meta, flags);

            if (err == OK) {
                return codec;
            }

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