寻找视频流的第一帧

int videoStream = -1;
for (int i = 0; i < pFormatCtx->nb_streams; i++) {
    if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
       && videoStream < 0) {
        videoStream = i;
    }
}

======》

int videoStream = -1;
for (int i = 0; i < pFormatCtx->nb_streams; i++) {
    if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO && videoStream < 0){
        videoStream = i;
    }
}

获取codec上下文指针

AVCodecContext  * pCodecCtx = pFormatCtx->streams[videoStream]->codec;

======》

AVCodecContext *pCodecCtx = avcodec_alloc_context3(NULL);
if (pCodecCtx == NULL)
{
    printf("Could not allocate AVCodecContext\n");
    return -1;
}
avcodec_parameters_to_context(pCodecCtx, pFormatCtx->streams[videoStream]->codecpar);

对该帧进行解码

while(av_read_frame(pFormatCtx, &packet)>=0) {
    //判断是否为视频流
    if(packet.stream_index==videoStream) {
        //对该帧进行解码，该方法已经过时弃用
        avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
        if (frameFinished) {
            // lock native window
            ANativeWindow_lock(nativeWindow, &windowBuffer, 0);
            // 格式转换
            sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data,
                      pFrame->linesize, 0, pCodecCtx->height,
                      pFrameRGBA->data, pFrameRGBA->linesize);
            // 获取stride
            uint8_t * dst = windowBuffer.bits;
            int dstStride = windowBuffer.stride * 4;
            uint8_t * src = pFrameRGBA->data[0];
            int srcStride = pFrameRGBA->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 < videoHeight; h++) {
                memcpy(dst + h * dstStride, src + h * srcStride, (size_t) srcStride);
            }
            ANativeWindow_unlockAndPost(nativeWindow);
        }
        //延迟等待
        usleep((unsigned long) (1000 * 40 * play_rate));
    }
    av_packet_unref(&packet);
}

======》

while (av_read_frame(pFormatCtx,&packet) >= 0){
    //判断是否为视频流
    if (packet.stream_index == videoStream) {
        //解码该帧
        if (avcodec_send_packet(pCodecCtx,&packet) == 0) {
            // 一个avPacket可能包含多帧数据，所以需要使用while循环一直读取
            while (avcodec_receive_frame(pCodecCtx,pFrame) == 0){
                // 1.lock window
                // 设置缓冲区的属性：宽高、像素格式（需要与Java层的格式一致）
                ANativeWindow_setBuffersGeometry(nativeWindow,videoWidth,videoHeight,WINDOW_FORMAT_RGBA_8888);
                ANativeWindow_lock(nativeWindow,&windowBuffer,NULL);
                // 格式转换
                sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data,
                          pFrame->linesize, 0, pCodecCtx->height,
                          pFrameRGBA->data, pFrameRGBA->linesize);

                // 获取stride
                uint8_t *dst =(uint8_t *) windowBuffer.bits;
                int dstStride = windowBuffer.stride * 4;
                uint8_t * src = pFrameRGBA->data[0];
                int srcStride = pFrameRGBA->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 < videoHeight; h++) {
                    memcpy(dst + h * dstStride, src + h * srcStride, (size_t) srcStride);
                }
                ANativeWindow_unlockAndPost(nativeWindow);
            }
        } else {
            LOGE("Error sending a packet for decoding");
            return -1;
        }
        // 每绘制一帧便休眠16毫秒，避免绘制过快导致播放的视频速度加快
        usleep(1000 * 16);
    }
    av_packet_unref(&packet);
}

编码参数上下文的拷贝

ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
if (ret < 0){
    printf("Failed to copy context from input to output stream codec context\n");
    goto end;
}
 
out_stream->codec->codec_tag = 0;
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
    out_stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;

======》

AVCodecContext *codec_ctx = avcodec_alloc_context3(in_codec);
ret = avcodec_parameters_to_context(codec_ctx, in_stream->codecpar);
if (ret < 0){
    printf("Failed to copy in_stream codecpar to codec context\n");
    goto end;
}
 
codec_ctx->codec_tag = 0;
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
    codec_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
 
ret = avcodec_parameters_from_context(out_stream->codecpar, codec_ctx);
if (ret < 0){
    printf("Failed to copy codec context to out_stream codecpar context\n");
    goto end;
}