Android 使用c++MediaCodec 解码例子

以下是使用C++ MediaCodec 进行视频解码的示例代码：

#include <jni.h>
#include <android/log.h>
#include <android/native_window_jni.h>
#include <media/NdkMediaCodec.h>
#include <media/NdkMediaExtractor.h>

#define LOG_TAG "MediaCodec"
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)

extern "C" JNIEXPORT void JNICALL
Java_com_example_mediadecoder_MainActivity_decode(JNIEnv *env, jobject thiz, jstring filePath, jobject surface) {
    const char *path = env->GetStringUTFChars(filePath, nullptr);

    AMediaExtractor *extractor = AMediaExtractor_new();
    AMediaCodec *codec = nullptr;
    int32_t trackIndex = -1;
    bool sawInputEOS = false;
    bool sawOutputEOS = false;

    // 设置文件路径
    media_status_t result = AMediaExtractor_setDataSource(extractor, path);
    if (result != AMEDIA_OK) {
        LOGE("AMediaExtractor_setDataSource error: %d", result);
        goto end;
    }

    // 查找视频轨道
    int32_t numTracks = AMediaExtractor_getTrackCount(extractor);
    for (int32_t i = 0; i < numTracks; ++i) {
        AMediaFormat *format = AMediaExtractor_getTrackFormat(extractor, i);
        const char *mime = nullptr;
        AMediaFormat_getString(format, AMEDIAFORMAT_KEY_MIME, &mime);
        if (mime && !strncmp(mime, "video/", 6)) {
            trackIndex = i;
            break;
        }
        AMediaFormat_delete(format);
    }

    if (trackIndex == -1) {
        LOGE("No video track found in %s", path);
        goto end;
    }

    // 获取视频格式
    AMediaFormat *format = AMediaExtractor_getTrackFormat(extractor, trackIndex);
    int32_t width = 0, height = 0;
    AMediaFormat_getInt32(format, AMEDIAFORMAT_KEY_WIDTH, &width);
    AMediaFormat_getInt32(format, AMEDIAFORMAT_KEY_HEIGHT, &height);
    LOGI("Video size: %dx%d", width, height);

    // 创建 MediaCodec 解码器
    codec = AMediaCodec_createDecoderByType("video/avc");
    result = AMediaCodec_configure(codec, format, ANativeWindow_fromSurface(env, surface), nullptr, 0);
    if (result != AMEDIA_OK) {
        LOGE("AMediaCodec_configure error: %d", result);
        goto end;
    }

    // 启动解码器
    result = AMediaCodec_start(codec);
    if (result != AMEDIA_OK) {
        LOGE("AMediaCodec_start error: %d", result);
        goto end;
    }

    // 解码视频帧
    AMediaCodecBufferInfo bufferInfo;
    int64_t presentationTimeUs;
    size_t bufIdx;
    while (!sawOutputEOS) {
        if (!sawInputEOS) {
            bufIdx = AMediaExtractor_getSampleTrackIndex(extractor);
            if (bufIdx == trackIndex) {
                result = AMediaExtractor_readSampleData(extractor, AMediaCodec_getInputBuffer(codec, bufIdx), 0);
                if (result == AMEDIA_OK) {
                    presentationTimeUs = AMediaExtractor_getSampleTime(extractor);
                    AMediaCodec_queueInputBuffer(codec, bufIdx, 0, AMediaExtractor_getSampleSize(extractor), presentationTimeUs,
                            AMediaExtractor_getSampleFlags(extractor));
                    AMediaExtractor_advance(extractor);
                } else if (result == AMEDIA_ERROR_END_OF_STREAM) {
                    sawInputEOS = true;
                    AMediaCodec_queueInputBuffer(codec, bufIdx, 0, 0, 0, AMEDIACODEC_BUFFER_FLAG_END_OF_STREAM);
                } else {
                    LOGE("AMediaExtractor_readSampleData error: %d", result);
                    goto end;
                }
            }
        }

        result = AMediaCodec_dequeueOutputBuffer(codec, &bufferInfo, 5000);
        if (result == AMEDIA_OK) {
            if (bufferInfo.flags & AMEDIACODEC_BUFFER_FLAG_END_OF_STREAM) {
                sawOutputEOS = true;
            }
            AMediaCodec_releaseOutputBuffer(codec, result, true);
        } else if (result == AMEDIACODEC_INFO_OUTPUT_FORMAT_CHANGED) {
            AMediaFormat *newFormat = nullptr;
            newFormat = AMediaCodec_getOutputFormat(codec);
            AMediaFormat_getInt32(newFormat, AMEDIAFORMAT_KEY_WIDTH, &width);
            AMediaFormat_getInt32(newFormat, AMEDIAFORMAT_KEY_HEIGHT, &height);
            LOGI("Video output format changed to %dx%d", width, height);
            AMediaFormat_delete(newFormat);
        } else if (result == AMEDIACODEC_INFO_OUTPUT_BUFFERS_CHANGED) {
            LOGI("AMediaCodec_dequeueOutputBuffer returned AMEDIACODEC_INFO_OUTPUT_BUFFERS_CHANGED");
        } else {
            LOGE("AMediaCodec_dequeueOutputBuffer error: %d", result);
            goto end;
        }
    }

    end:
    if (codec) {
        AMediaCodec_stop(codec);
        AMediaCodec_delete(codec);
    }
    if (extractor) {
        AMediaExtractor_delete(extractor);
    }
    env->ReleaseStringUTFChars(filePath, path);
}

在此示例代码中，我们使用 `AMediaExtractor` 获取视频文件中的视频轨道，并使用 `AMediaCodec` 进行解码。注意，此代码仅支持解码 H.264 编码视频。