ffmpeg实战教程（二）用SDL播放YUV，并结合ffmpeg实现简易播放器

我们先实现用SDL播放YUV数据

先来了解一下基本概念

SDL基本函数：
[初始化]
* SDL_Init(): 初始化SDL。
* SDL_CreateWindow(): 创建窗口（Window）。
* SDL_CreateRenderer(): 基于窗口创建渲染器（Render）。
* SDL_CreateTexture(): 创建纹理（Texture）。

[循环渲染数据]
* SDL_UpdateTexture(): 设置纹理的数据。
* SDL_RenderCopy(): 纹理复制给渲染器。
* SDL_RenderPresent(): 显示。

C中的fseek函数
int fseek( FILE *stream, long offset, int origin );
第一个参数stream为文件指针
第二个参数offset为偏移量，整数表示正向偏移，负数表示负向偏移
第三个参数origin设定从文件的哪里开始偏移,可能取值为：SEEK_CUR、 SEEK_END 或 SEEK_SET
SEEK_SET： 文件开头
SEEK_CUR： 当前位置
SEEK_END： 文件结尾
其中SEEK_SET,SEEK_CUR和SEEK_END和依次为0，1和2.
简言之：
fseek(fp,100L,0);把fp指针移动到离文件开头100字节处；
fseek(fp,100L,1);把fp指针移动到离文件当前位置100字节处；
fseek(fp,100L,2);把fp指针退回到离文件结尾100字节处。

下面看一下运行效果：

下面看源代码 注释很详细

#include <stdio.h>

extern "C"
{
#include "sdl/SDL.h"
};

const int bpp=12;

int screen_w=500,screen_h=500;
const int pixel_w=1920,pixel_h=1080;

unsigned char buffer[pixel_w*pixel_h*bpp/8];


//Refresh Event
#define REFRESH_EVENT  (SDL_USEREVENT + 1)

#define BREAK_EVENT  (SDL_USEREVENT + 2)

int thread_exit=0;

int refresh_video(void *opaque){
    thread_exit=0;
    while (!thread_exit) {
        SDL_Event event;
        event.type = REFRESH_EVENT;
        SDL_PushEvent(&event); //发送事件 即handler
        SDL_Delay(40);
    }
    thread_exit=0;
    //Break
    SDL_Event event;//代表一个事件 声明
    event.type = BREAK_EVENT;
    SDL_PushEvent(&event);

    return 0;
}

int main(int argc, char* argv[])
{
    if(SDL_Init(SDL_INIT_VIDEO)) {  //初始化SDL系统
        printf( "Could not initialize SDL - %s\n", SDL_GetError()); 
        return -1;
    } 

    SDL_Window *screen; 
    //SDL 2.0  创建窗口（Window）。
    screen = SDL_CreateWindow("WS Video Play SDL2", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
        screen_w, screen_h,SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
    if(!screen) {  
        printf("SDL: could not create window - exiting:%s\n",SDL_GetError());  
        return -1;
    }
    //创建基于窗口创建渲染器（Render）
    SDL_Renderer* sdlRenderer = SDL_CreateRenderer(screen, -1, 0);  

    Uint32 pixformat=0;

    //IYUV: Y + U + V  (3 planes)
    //YV12: Y + V + U  (3 planes)
    pixformat= SDL_PIXELFORMAT_IYUV;  
    //创建纹理（Texture）
    SDL_Texture* sdlTexture = SDL_CreateTexture(sdlRenderer,pixformat, SDL_TEXTUREACCESS_STREAMING,pixel_w,pixel_h);

    FILE *fp=NULL;
    //用我们上篇博客解码出来的yuv文件
    fp=fopen("output.yuv","rb+");

    if(fp==NULL){
        printf("cannot open this file\n");
        return -1;
    }
    //window 视频显示框
    SDL_Rect sdlRect;  

    SDL_Thread *refresh_thread = SDL_CreateThread(refresh_video,NULL,NULL);//创建线程
    SDL_Event event;
    while(1){
        //Wait等待事件 即监听
        SDL_WaitEvent(&event);
        if(event.type==REFRESH_EVENT){
            if (fread(buffer, 1, pixel_w*pixel_h*bpp/8, fp) != pixel_w*pixel_h*bpp/8){
                // Loop
                fseek(fp, 0, SEEK_SET);
                fread(buffer, 1, pixel_w*pixel_h*bpp/8, fp);
            }
            //设置纹理的数据
            SDL_UpdateTexture( sdlTexture, NULL, buffer, pixel_w);  

            //FIX: If window is resize
            sdlRect.x = 0;  
            sdlRect.y = 0;  
            sdlRect.w = screen_w;  
            sdlRect.h = screen_h;  

            SDL_RenderClear( sdlRenderer ); 
            //将纹理的数据拷贝给渲染器
            SDL_RenderCopy( sdlRenderer, sdlTexture, NULL, &sdlRect);  
            //显示
            SDL_RenderPresent( sdlRenderer );  

        }else if(event.type==SDL_WINDOWEVENT){
            //If Resize SDL_WINDOWEVENT事件 可以拉伸播放器界面
            SDL_GetWindowSize(screen,&screen_w,&screen_h);
        }else if(event.type==SDL_QUIT){
            thread_exit=1;
        }else if(event.type==BREAK_EVENT){
            break;
        }
    }
    SDL_Quit();//退出系统
    return 0;
}

我们把上篇博客解码出来的YUV数据拷贝到项目跟目录，然后编译运行即可
配置环境以及编译运行部分看 此系列的实战（一）
http://blog.csdn.net/king1425/article/details/71160339

下面我们结合上篇博客 把MP4解码为YUV，然后在SDL上播放。这样一个简易版的视频播放器就出现了

我们把一个MP4文件拷贝到项目跟目录 命名为ws.mp4
然后运行源码文件
看效果图：

#include <stdio.h>

#define __STDC_CONSTANT_MACROS

#ifdef _WIN32
//Windows
extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "SDL2/SDL.h"
};
#else
//Linux...
#ifdef __cplusplus
extern "C"
{
#endif
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
#include <SDL2/SDL.h>
#ifdef __cplusplus
};
#endif
#endif

//Refresh Event
#define SFM_REFRESH_EVENT  (SDL_USEREVENT + 1)

#define SFM_BREAK_EVENT  (SDL_USEREVENT + 2)

int thread_exit=0;
int thread_pause=0;

int sfp_refresh_thread(void *opaque){
    thread_exit=0;
    thread_pause=0;

    while (!thread_exit) {
        if(!thread_pause){
            SDL_Event event;
            event.type = SFM_REFRESH_EVENT;
            SDL_PushEvent(&event);
        }
        SDL_Delay(40);
    }
    thread_exit=0;
    thread_pause=0;
    //Break
    SDL_Event event;
    event.type = SFM_BREAK_EVENT;
    SDL_PushEvent(&event);

    return 0;
}


int main(int argc, char* argv[])
{

    AVFormatContext *pFormatCtx;
    int             i, videoindex;
    AVCodecContext  *pCodecCtx;
    AVCodec         *pCodec;
    AVFrame *pFrame,*pFrameYUV;
    uint8_t *out_buffer;
    AVPacket *packet;
    int ret, got_picture;

    //------------SDL----------------
    int screen_w,screen_h;
    SDL_Window *screen; 
    SDL_Renderer* sdlRenderer;
    SDL_Texture* sdlTexture;
    SDL_Rect sdlRect;
    SDL_Thread *video_tid;
    SDL_Event event;

    struct SwsContext *img_convert_ctx;

    char filepath[]="ws.mp4";

    av_register_all();
    avformat_network_init();
    pFormatCtx = avformat_alloc_context();

    if(avformat_open_input(&pFormatCtx,filepath,NULL,NULL)!=0){
        printf("Couldn‘t open input stream.\n");
        return -1;
    }
    if(avformat_find_stream_info(pFormatCtx,NULL)<0){
        printf("Couldn‘t find stream information.\n");
        return -1;
    }
    videoindex=-1;
    for(i=0; i<pFormatCtx->nb_streams; i++) 
        if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
            videoindex=i;
            break;
        }
    if(videoindex==-1){
        printf("Didn‘t find a video stream.\n");
        return -1;
    }
    pCodecCtx=pFormatCtx->streams[videoindex]->codec;
    pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
    if(pCodec==NULL){
        printf("Codec not found.\n");
        return -1;
    }
    if(avcodec_open2(pCodecCtx, pCodec,NULL)<0){
        printf("Could not open codec.\n");
        return -1;
    }
    pFrame=av_frame_alloc();
    pFrameYUV=av_frame_alloc();
    out_buffer=(uint8_t *)av_malloc(avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));
    avpicture_fill((AVPicture *)pFrameYUV, out_buffer, PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);

    //Output Info-----------------------------
    printf("---------------- File Information ---------------\n");
    av_dump_format(pFormatCtx,0,filepath,0);
    printf("-------------------------------------------------\n");

    img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, 
        pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL); 


    if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {  
        printf( "Could not initialize SDL - %s\n", SDL_GetError()); 
        return -1;
    } 
    //SDL 2.0 Support for multiple windows
    screen_w = pCodecCtx->width;
    screen_h = pCodecCtx->height;
    screen = SDL_CreateWindow("WS ffmpeg player", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
        500, 500,SDL_WINDOW_OPENGL);

    if(!screen) {  
        printf("SDL: could not create window - exiting:%s\n",SDL_GetError());  
        return -1;
    }
    sdlRenderer = SDL_CreateRenderer(screen, -1, 0);  
    //IYUV: Y + U + V  (3 planes)
    //YV12: Y + V + U  (3 planes)
    sdlTexture = SDL_CreateTexture(sdlRenderer, SDL_PIXELFORMAT_IYUV, SDL_TEXTUREACCESS_STREAMING,pCodecCtx->width,pCodecCtx->height);  

    sdlRect.x=0;
    sdlRect.y=0;
    sdlRect.w=screen_w;
    sdlRect.h=screen_h;

    packet=(AVPacket *)av_malloc(sizeof(AVPacket));

    video_tid = SDL_CreateThread(sfp_refresh_thread,NULL,NULL);
    //------------SDL End------------
    //Event Loop

    for (;;) {
        //Wait
        SDL_WaitEvent(&event);
        if(event.type==SFM_REFRESH_EVENT){
            //------------------------------
            if(av_read_frame(pFormatCtx, packet)>=0){
                if(packet->stream_index==videoindex){
                    ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
                    if(ret < 0){
                        printf("Decode Error.\n");
                        return -1;
                    }
                    if(got_picture){
                        sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);
                        //SDL---------------------------
                        SDL_UpdateTexture( sdlTexture, NULL, pFrameYUV->data[0], pFrameYUV->linesize[0] );  
                        SDL_RenderClear( sdlRenderer );  
                        //SDL_RenderCopy( sdlRenderer, sdlTexture, &sdlRect, &sdlRect );  
                        SDL_RenderCopy( sdlRenderer, sdlTexture, NULL, NULL);  
                        SDL_RenderPresent( sdlRenderer );  
                        //SDL End-----------------------
                    }
                }
                av_free_packet(packet);
            }else{
                //Exit Thread
                thread_exit=1;
            }
        }else if(event.type==SDL_KEYDOWN){
            //Pause
            if(event.key.keysym.sym==SDLK_SPACE)
                thread_pause=!thread_pause;
        }else if(event.type==SDL_QUIT){
            thread_exit=1;
        }else if(event.type==SFM_BREAK_EVENT){
            break;
        }

    }

    sws_freeContext(img_convert_ctx);

    SDL_Quit();
    //--------------
    av_frame_free(&pFrameYUV);
    av_frame_free(&pFrame);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}