FFmpeg学习记录（四）——SDL音视频渲染实战

1.SDL使用的基本步骤

• SDL Init/sDL _Quit()
• SDL_CreateWindow()/SDL_DestoryWindow()
• SDL CreateRender()

    SDL_Windows *windows = NULL;

    SDL_Init(SDL_INIT_VIDEO);

    window = SDL_CreateWindow("SDL2 Windows",
                             200,
                             200, 640,
                             480,
                             SDL_WINDOW_SHOWN);

    if(!window) {
        printf("Couldn't create window\n");
        goto __EXIT;
    }

    SDL_DestroyWindow(window);

__EXIT:
    SDL_Quit();

2.SDL窗口渲染

SDL渲染窗口

• SDL _CreateRender/SDL_DestoryRenderer
• SDL RenderClear
• SDL RenderPresent

 render = SDL_CreateRenderer(window, -1, 0);
    if(!render) {
        SDL_Log("Failed to create renderer\n");
        goto __DWINDOW;
    }

    SDL_SetRenderDrawColor(render, 255, 0, 0, 255);
    SDL_RenderClear(render);
    SDL_RenderPresent(render);
    SDL_Delay(5000);


__DWINDOW:
    SDL_DestroyWindow(window);

3.SDL事件

SDL事件基本原理

• SDL将所有事件都存放在一个队列中
• 所有对事件的操作，其实就是对队列的操作

SDL事件种类

• SDL WindowEvent:窗口事件
• SDL_KeyboardEvent:键盘事件
• SDL MouseMotionEvent:鼠标事件
• 自定义事件

    do{
        SDL_Event event;
        SDL_WaitEvent(&event);
        switch(event.type) {
            case SDL_QUIT:
                quit = 0;
                break;
            default:
                SDL_Log("event type is %d\n", event.type);
        }
    }while(quit);

4.纹理渲染

SDL纹理相关 API

• SDL CreateTexture()
  format : YUV, RGBaccess :Texture类型，Target,Stream
• SDL_DestroyTexture()

SDL渲染相关API

• SDL SetRenderTarget()
• SDL _RenderClear()
• SDL_RenderCopy()
• SDL RenderPresent()

到此终于可以写出完整版代码了：

#include <stdio.h>
#include <SDL.h>


int main(int argc, char const *argv[])
{
    SDL_Windows *windows = NULL;
    SDL_Renderer *renderer = NULL;

    int quit = 1;
    SDL_Texture *texture = NULL;
    SDL_Rect rect;
    rect.w = 30;
    rect.h = 30;

    window = SDL_CreateWindow("SDL2 Windows",
                             200,
                             200, 640,
                             480,
                             SDL_WINDOW_SHOWN);

    if(!window) {
        printf("Couldn't create window\n");
        goto __EXIT;
    }

    render = SDL_CreateRenderer(window, -1, 0);
    if(!render) {
        SDL_Log("Failed to create renderer\n");
        goto __DWINDOW;
    }

    // SDL_SetRenderDrawColor(render, 255, 0, 0, 255);
    // SDL_RenderClear(render);
    // SDL_RenderPresent(render);

    texture = SDL_CreateTexture(render, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET,640,480);
    if(!texture){
        SDL_Log("Failed to Create Texture!\n");
        goto _RENDER;
    }

    do{
        SDL_Event event;
        // SDL_WaitEvent(&event);
        SDL_PollEvent(&event);
        switch(event.type) {
            case SDL_QUIT:
                quit = 0;
                break;
            default:
                SDL_Log("event type is %d\n", event.type);
        }

        rect.x = rand() % 640;
        rect.y = rand() % 480;
		
        SDL_SetRenderTarget(render, texture);
        SDL_SetRenderDrawColor(render, 0, 0, 0, 0);
        SDL_RenderClear(render);

        SDL_RenderDrawRect(render, &rect);
        SDL_SetRenderDrawColor(render, 255, 0, 0, 0);
        SDL_RenderFillRect(render, &rect);

        SDL_SetRenderTarget(render, NULL);
        SDL_RenderCopy(render, texture, NULL, NULL);

        SDL_RenderPresent(render);

    }while(quit);


    SDL_DestroyTexture(texture);

_RENDER:
    SDL_DestroyRenderer(render);

__DWINDOW:
    SDL_DestroyWindow(window);

__EXIT:
    SDL_Quit();


    return 0;
}

5.YUV视频播放器

创建线程

• SDL_CreateThread
  fn:线程执行函数
  name:线程名
  data:执行函数参数

SDL更新纹理

• SDL_UpdateTexutre()
• SDL_UpdateYUVTexture()

核心代码：

    do {
        //Wait
        SDL_WaitEvent(&event);
        if(event.type==REFRESH_EVENT){
            //not enought data to render
            if((video_pos + yuv_frame_len) > video_end){

                //have remain data, but there isn't space
                remain_len = video_end - video_pos;
                if(remain_len && !blank_space_len) {
                    //copy data to header of buffer
                    memcpy(video_buf, video_pos, remain_len);

                    blank_space_len = BLOCK_SIZE - remain_len;
                    video_pos = video_buf;
                    video_end = video_buf + remain_len;
                }

                //at the end of buffer, so rotate to header of buffer
                if(video_end == (video_buf + BLOCK_SIZE)){
                    video_pos = video_buf;
                    video_end = video_buf;
                    blank_space_len = BLOCK_SIZE;
                }

                //read data from yuv file to buffer
                if((video_buff_len = fread(video_end, 1, blank_space_len, video_fd)) <= 0){
                    fprintf(stderr, "eof, exit thread!");
                    thread_exit = 1;
                    continue;// to wait event for exiting
                }

                //reset video_end
                video_end += video_buff_len;
                blank_space_len -= video_buff_len;
                printf("not enought data: pos:%p, video_end:%p, blank_space_len:%d\n", video_pos, video_end, blank_space_len);
            }

            SDL_UpdateTexture( texture, NULL, video_pos, video_width);

            //FIX: If window is resize
            rect.x = 0;
            rect.y = 0;
            rect.w = w_width;
            rect.h = w_height;

            SDL_RenderClear( renderer );
            SDL_RenderCopy( renderer, texture, NULL, &rect);
            SDL_RenderPresent( renderer );

            printf("not enought data: pos:%p, video_end:%p, blank_space_len:%d\n", video_pos, video_end, blank_space_len);
            video_pos += yuv_frame_len;

        }else if(event.type==SDL_WINDOWEVENT){
            //If Resize
            SDL_GetWindowSize(win, &w_width, &w_height);
        }else if(event.type==SDL_QUIT){
            thread_exit=1;
        }else if(event.type==QUIT_EVENT){
            break;
        }
    }while ( 1 );

6.PCM音频播放器

播放音频的基本原则

• 声卡向你要数据而不是你主动推给声卡
• 数据的多少由音频参数决定的

SDL音频API

• SDL_OpenAudio/SDL_CloseAudio
• SDL PauseAudio
• SDL MixAudio

    //SDL initialize
    if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)){
        fprintf(stderr, "Could not initialize SDL - %s\n", SDL_GetError());
        return ret;
    }

    //open pcm file
    audio_fd = fopen(path, "rb");
    if(!audio_fd){
        fprintf(stderr, "Failed to open pcm file!\n");
        goto __FAIL;
    }

    //alloc memory for audio
    audio_buf = (Uint8*)malloc(BLOCK_SIZE);
    if(!audio_buf){
        goto __FAIL;
    }

    //SDL_AudioSpec
    spec.freq = 44100;;
    spec.format = AUDIO_S16SYS;
    spec.channels = 2;
    spec.silence = 0;
    spec.samples = 1024;
    spec.callback = read_audio_data;;
    spec.userdata = NULL;

    //open audio devcie
    if(SDL_OpenAudio(&spec, NULL)){
        fprintf(stderr, "Failed to open audio device, %s\n", SDL_GetError());
        goto __FAIL;
    }

    //play audio
    SDL_PauseAudio(0);

    do{
        //read data from pcm file
        buffer_len = fread(audio_buf, 1, BLOCK_SIZE, audio_fd);
        fprintf(stderr, "block size is %zu\n", buffer_len);

        audio_pos = audio_buf;

        //the main thread wait for a moment
        while(audio_pos < (audio_buf + buffer_len)) {
            SDL_Delay(1);
        }

    }while(buffer_len !=0);

    //close audio device
    SDL_CloseAudio();

    ret = 0;

//callback function for audio devcie
void read_audio_data(void *udata, Uint8 *stream, int len){

    if(buffer_len == 0){
        return;
    }

    SDL_memset(stream, 0, len);

    len = (len < buffer_len) ? len : buffer_len;
    printf("len=%d\n", len);
    SDL_MixAudio(stream, audio_pos, len, SDL_MIX_MAXVOLUME);

    audio_pos += len;
    buffer_len -= len;
}