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 {//WaitSDL_WaitEvent(&event);if(event.type==REFRESH_EVENT){//not enought data to renderif((video_pos + yuv_frame_len) > video_end){//have remain data, but there isn't spaceremain_len = video_end - video_pos;if(remain_len && !blank_space_len) {//copy data to header of buffermemcpy(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 bufferif(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 bufferif((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_endvideo_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 resizerect.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 ResizeSDL_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

在这里插入图片描述
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 initializeif(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 fileaudio_fd = fopen(path, "rb");if(!audio_fd){fprintf(stderr, "Failed to open pcm file!\n");goto __FAIL;}//alloc memory for audioaudio_buf = (Uint8*)malloc(BLOCK_SIZE);if(!audio_buf){goto __FAIL;}//SDL_AudioSpecspec.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 devcieif(SDL_OpenAudio(&spec, NULL)){fprintf(stderr, "Failed to open audio device, %s\n", SDL_GetError());goto __FAIL;}//play audioSDL_PauseAudio(0);do{//read data from pcm filebuffer_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 momentwhile(audio_pos < (audio_buf + buffer_len)) {SDL_Delay(1);}}while(buffer_len !=0);//close audio deviceSDL_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;
}