FFmpeg视频解码播放

在上篇文章中讲到了FFmpeg解码音频，对于FFmpeg解码视频与音频解码流程大致相同。其区别在于播放的方式与逻辑。我们可以利用c++面向对象的思想抽离出来很多工作流程相同的代码。对于音频来说重采样和播放，对于视频来说将数据转换缩放等渲染有特定逻辑。这里我们采用的是Android原生SurfaceView渲染画面

extern "C"
JNIEXPORT void JNICALL
Java_com_youyangbo_media_FFplayer_nStart(JNIEnv *env, jobject instance,jstring _url，jobject surface) {
  const char *url = env->GetStringUTFChars(url_, 0);
   av_register_all();
    avformat_network_init();
    AVFormatContext *pFormatContext = avformat_alloc_context();
    int open_result = avformat_open_input(&pFormatContext, url, NULL, NULL);
    LOGE("url = %s", url);
    if (open_result != 0) {
        LOGE("打开媒体文件失败");
        return;
    }

    int find_stream_result = avformat_find_stream_info(pFormatContext, NULL);
    if (find_stream_result < 0) {
        LOGE("查找流信息失败");
        return;
    }

    int video_index = av_find_best_stream(pFormatContext, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);

    AVCodecParameters *pCodecParameters = pFormatContext->streams[video_index]->codecpar;
    AVCodec *pCodec = avcodec_find_decoder(
            pFormatContext->streams[video_index]->codecpar->codec_id);

    AVCodecContext *pCodecContext = avcodec_alloc_context3(pCodec);
    int avcodec_parameters_to_context_result = avcodec_parameters_to_context(
            pCodecContext,
            pCodecParameters);


    int open_codec_result = avcodec_open2(pCodecContext, pCodec, NULL);
    if (open_codec_result != 0) {
        LOGE("打开解码器失败");
        return;
    }


    AVFrame * pRgbaFrame = av_frame_alloc();
    int frameSize = av_image_get_buffer_size(AV_PIX_FMT_RGBA, pCodecContext->width,
                                             pCodecContext->height, 1);
    uint8_t * pFrameBuffer = (uint8_t *) malloc(frameSize);
    av_image_fill_arrays(pRgbaFrame->data, pRgbaFrame->linesize, pFrameBuffer, AV_PIX_FMT_RGBA,
                         pCodecContext->width, pCodecContext->height, 1);


    // 1. 获取窗体
    ANativeWindow *pNativeWindow = ANativeWindow_fromSurface(env, surface);

    // 2. 设置缓存区的数据
    ANativeWindow_setBuffersGeometry(pNativeWindow, pCodecContext->width,
                                     pCodecContext->height, WINDOW_FORMAT_RGBA_8888);
    // Window 缓冲区的 Buffer
    ANativeWindow_Buffer outBuffer;
    //这里最好定义变量
    while (true) {
        AVPacket *pkt = av_packet_alloc();
        if (av_read_frame(pFormatContext, pkt) == 0) {
            if (pkt->stream_index == video_index ) {

                if (avcodec_send_packet(pCodecContext , pkt) == 0) {
                    AVFrame *pFrame = av_frame_alloc();
                    if (avcodec_receive_frame(pCodecContext , pFrame) == 0) {
                        //解出Frame数据
                        ANativeWindow_lock(pNativeWindow, &outBuffer, NULL);
                        libyuv::I420ToARGB(pFrame->data[0],
                                           pFrame->linesize[0],
                                           pFrame->data[2],
                                           pFrame->linesize[2],
                                           pFrame->data[1],
                                           pFrame->linesize[1],
                                           pRgbaFrame->data[0],
                                           pRgbaFrame->linesize[0],
                                           pCodecContext->width,
                                           pCodecContext->height);


                        // 获取stride
                        int dstStride = outBuffer.stride * 4;
                        uint8_t *src = (pRgbaFrame->data[0]);
                        int srcStride = pRgbaFrame->linesize[0];

                        // 由于window的stride和帧的stride不同,因此需要逐行复制
                        int h;
                        for (h = 0; h < pCodecContext->height; h++) {
                            memcpy((u_int8_t*)outBuffer.bits + h * dstStride, src + h * srcStride, srcStride);
                        }


                        // 把数据推到缓冲区
                        ANativeWindow_unlockAndPost(pNativeWindow);

                        av_frame_unref(pFrame);
                        av_frame_free(&pFrame);
                        av_packet_unref(pkt);
                        av_packet_free(&pkt);

                    } else {
                        av_frame_unref(pFrame);
                        av_frame_free(&pFrame);
                        av_packet_unref(pkt);
                        av_packet_free(&pkt);
                    }

                } else {
                    av_packet_unref(pkt);
                    av_packet_free(&pkt);

                }


            }

        } else {
            av_packet_unref(pkt);
            av_packet_free(&pkt);
            break;
        }

    }
env->ReleaseStringUTFChars(url_, url);
}

上述代码中引用了libyuv库，libyuv是Google开源的实现各种YUV与RGB之间相互转换、旋转、缩放的库。简单的介绍一下libyuv库的编译。
libyuv:源码 https://github.com/lemenkov/libyuv
libyuv作为一个NDK项目，必须满足有jni文件夹 与 Application.mk文件，所以我们新建jni目录将libyuv 的源码放入其下，在Android.mk文件同级目录下创建Application.mk文件

#Application.mk 文件内容
APP_ABI := armeabi x86
APP_PLATFORM := android-16
APP_ALLOW_MISSING_DEPS=true
APP_STL := stlport_static
APP_CPPFLAGS += -fno-rtti

然后直接敲ndk-build命令就可以完成libyuv的编译。在jni目录下会生成libs目录包含我们所需动态库。
编译的过程中可能会报一些关于JPEG错,将Android.mk文件中JPEG部分注掉就可以成功编译

# Android.mk文件
# This is the Android makefile for libyuv for NDK.
LOCAL_PATH:= $(call my-dir)

include $(CLEAR_VARS)

LOCAL_CPP_EXTENSION := .cc

.............省略.............

common_CFLAGS := -Wall -fexceptions
#ifneq ($(LIBYUV_DISABLE_JPEG), "yes")
#LOCAL_SRC_FILES += \
#    source/convert_jpeg.cc      \
#    source/mjpeg_decoder.cc     \
#    source/mjpeg_validate.cc
#common_CFLAGS += -DHAVE_JPEG
#LOCAL_SHARED_LIBRARIES := libjpeg
#endif

LOCAL_CFLAGS += $(common_CFLAGS)
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include
LOCAL_C_INCLUDES += $(LOCAL_PATH)/include
LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include

LOCAL_MODULE := libyuv_static
LOCAL_MODULE_TAGS := optional

include $(BUILD_STATIC_LIBRARY)

include $(CLEAR_VARS)

LOCAL_WHOLE_STATIC_LIBRARIES := libyuv_static
LOCAL_MODULE := libyuv
#ifneq ($(LIBYUV_DISABLE_JPEG), "yes")
#LOCAL_SHARED_LIBRARIES := libjpeg
#endif

include $(BUILD_SHARED_LIBRARY)

.............省略.............