输出格式video_output_open

video_output_open中创建并初始化video_t结构体：

struct video_output {
    struct video_output_info info;
    pthread_t thread;
    pthread_mutex_t data_mutex;
    bool stop;
    os_sem_t *update_semaphore;
    uint64_t frame_time;
    volatile long skipped_frames;
    volatile long total_frames;
    bool initialized;
    pthread_mutex_t input_mutex;
    DARRAY(struct video_input) inputs;
    size_t available_frames;
    size_t first_added;
    size_t last_added;
    struct cached_frame_info cache[MAX_CACHE_SIZE];//16个
    volatile bool raw_active;
    volatile long gpu_refs;
};
struct video_output;
typedef struct video_output video_t;

初始化后信息如下

缓冲帧cache的初始化如下：

static inline void init_cache(struct video_output *video)
{
    if (video->info.cache_size > MAX_CACHE_SIZE)
        video->info.cache_size = MAX_CACHE_SIZE;
    for (size_t i = 0; i < video->info.cache_size; i++)
    {
        struct video_frame* frame =(struct video_frame *)&video->cache[i];
        video_frame_init(frame, video->info.format, video->info.width, video->info.height);
    }
    video->available_frames = video->info.cache_size;
}

video_frame_init中根据格式和宽度进行初始化每个FRAME，这里至少一个（如RGB)或者三个(I420:YUV)或者二个(NV12:Y UV)

struct video_frame {
    uint8_t *data[MAX_AV_PLANES];
    uint32_t linesize[MAX_AV_PLANES];
};

如I420的代码格式如下：

    case VIDEO_FORMAT_I420: {
        size = width * height;
        ALIGN_SIZE(size, alignment);//32字节的整数倍速对齐
        offsets[0] = size;
        const uint32_t half_width = (width + 1) / 2;
        const uint32_t half_height = (height + 1) / 2;
        const uint32_t quarter_area = half_width * half_height;
        size += quarter_area;
        ALIGN_SIZE(size, alignment); //u起始地址32对齐
        offsets[1] = size;
        size += quarter_area;
        ALIGN_SIZE(size, alignment);/v起始地址32对齐
        frame->data[0] = bmalloc(size);
        frame->data[1] = (uint8_t *)frame->data[0] + offsets[0];
        frame->data[2] = (uint8_t *)frame->data[0] + offsets[1];
        frame->linesize[0] = width;
        frame->linesize[1] = half_width;
        frame->linesize[2] = half_width;
        break;
    }

32地址的对齐我记得是GPU的要求，所以这为了CPU和GPU之间进行地址映射方便。