给出android av中使用kKeyIsSyncFrame 的完整代码

以下是使用android av中的kKeyIsSyncFrame的完整代码示例：

#include <media/stagefright/MediaBuffer.h>
#include <media/stagefright/MediaCodec.h>
#include <media/stagefright/MediaExtractor.h>
#include <media/stagefright/Utils.h>

...

sp<MediaExtractor> extractor = MediaExtractor::Create(
        env, env->NewStringUTF(sourceUrl.c_str()));

// Find and select the first video track.
sp<MetaData> videoFormat;
ssize_t videoTrackIndex = -1;
for (size_t i = 0; i < extractor->countTracks(); ++i) {
    videoFormat = extractor->getTrackFormat(i);

    const char *mime;
    if (!videoFormat->findCString(kKeyMIMEType, &mime)) {
        continue;
    }

    if (!strncasecmp(mime, "video/", 6)) {
        videoTrackIndex = i;
        break;
    }
}

if (videoTrackIndex < 0) {
    // No video track found.
    return;
}

extractor->selectTrack(videoTrackIndex);

// Create a MediaCodec for decoding.
sp<MediaCodec> decoder = MediaCodec::CreateByType(
        env, videoFormat.get(), false /* encoder */, NULL /* crypto */);

decoder->configure(videoFormat.get(),
        surface /* output surface */,
        NULL /* crypto */,
        0 /* flags */);

decoder->start();

// Start decoding.
bool sawInputEOS = false;
bool sawOutputEOS = false;
while (!sawOutputEOS) {
    if (!sawInputEOS) {
        ssize_t inputBufIndex = decoder->dequeueInputBuffer(kTimeoutUs);
        if (inputBufIndex >= 0) {
            sp<MediaCodecBuffer> inputBuf = decoder->getInputBuffer(inputBufIndex);

            size_t sampleSize = extractor->readSampleData(inputBuf->data(), inputBuf->size());
            if (sampleSize < 0) {
                sawInputEOS = true;
                sampleSize = 0;
            }

            int64_t presentationTimeUs = extractor->getSampleTime();
            int32_t flags = extractor->getSampleFlags();
            if (flags & MediaExtractor::SAMPLE_FLAG_SYNC) {
                inputBuf->meta_data()->setInt32(kKeyIsSyncFrame, 1);
            } else {
                inputBuf->meta_data()->setInt32(kKeyIsSyncFrame, 0);
            }

            decoder->queueInputBuffer(
                    inputBufIndex,
                    0 /* offset */,
                    sampleSize,
                    presentationTimeUs,
                    flags);
            extractor->advance();
        }
    }

    MediaCodecBuffer *outBuf = NULL;
    MediaCodec::BufferInfo outInfo;
    ssize_t outBufIndex = decoder->dequeueOutputBuffer(&outBuf, &outInfo, kTimeoutUs);
    if (outBufIndex >= 0) {
        if (outInfo.flags & MediaCodec::BUFFER_FLAG_END_OF_STREAM) {
            sawOutputEOS = true;
        }

        decoder->releaseOutputBuffer(outBufIndex, outInfo.size != 0);
    } else if (outBufIndex == MediaCodec::INFO_OUTPUT_BUFFERS_CHANGED) {
        // The output buffers have changed, we need to get a new set.
    } else if (outBufIndex == MediaCodec::INFO_OUTPUT_FORMAT_CHANGED) {
        // The output format has changed, we need to use the new format and
        // possibly resize the video output surface.
        sp<MetaData> newFormat = decoder->getOutputFormat();
        decoder->configure(newFormat.get(), surface, NULL, 0);
    }
}

// Stop and release the decoder.
decoder->stop();
decoder->release();

在上述代码中，当从`MediaExtractor`读取视频帧时，如果该帧是同步帧（也就是关键帧），则会将`kKeyIsSyncFrame`元数据设置为1，否则设置为0，以便在解码后进行使用。