FFmpeg+SDL视频播放器代码学习
参考博客：https://blog.csdn.net/leixiaohua1020/article/details/38868499
1.仅对FFmpeg部分做了一部分注释
2.代码未作改动，只进行注释，仅为学习
/**
* 最简单的基于FFmpeg的视频播放器 2
* Simplest FFmpeg Player 2
*
* 雷霄骅 Lei Xiaohua
* leixiaohua1020@126.com
* 中国传媒大学/数字电视技术
* Communication University of China / Digital TV Technology
* http://blog.csdn.net/leixiaohua1020
*
* 第2版使用SDL2.0取代了第一版中的SDL1.2
* Version 2 use SDL 2.0 instead of SDL 1.2 in version 1.
*
* 本程序实现了视频文件的解码和显示(支持HEVC，H.264，MPEG2等)。
* 是最简单的FFmpeg视频解码方面的教程。
* 通过学习本例子可以了解FFmpeg的解码流程。
* This software is a simplest video player based on FFmpeg.
* Suitable for beginner of FFmpeg.
*
*/
//主要过程是解码的过程，其SDL过程暂时不看
#include <stdio.h>
#define __STDC_CONSTANT_MACROS
//如果是win32，应该包含的头文件
#ifdef _WIN32
//Windows
extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libavutil/imgutils.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>
#include <libavutil/imgutils.h>
#ifdef __cplusplus
};
#endif
#endif
//Output YUV420P data as a file
#define OUTPUT_YUV420P 0
int main(int argc, char* argv[])
{
AVFormatContext *pFormatCtx;
int i, videoindex;
AVCodecContext *pCodecCtx;
AVCodec *pCodec;
AVFrame *pFrame,*pFrameYUV;
unsigned char *out_buffer;
AVPacket *packet;
int y_size;
int ret, got_picture;
struct SwsContext *img_convert_ctx;
char filepath[]="bigbuckbunny_480x272.h265";
//SDL---------------------------
int screen_w=0,screen_h=0;
SDL_Window *screen;
SDL_Renderer* sdlRenderer;
SDL_Texture* sdlTexture;
SDL_Rect sdlRect;
FILE *fp_yuv;
av_register_all();//注册组件？现在这个函数的功能转移到哪里了
avformat_network_init();//网络的初始化
pFormatCtx = avformat_alloc_context();//AVFormat结构体内存分配 用于创建AVFormatContext
//调用avformat_open_input函数打开视频流==注意传入的参数
if(avformat_open_input(&pFormatCtx,filepath,NULL,NULL)!=0){
printf("Couldn't open input stream.\n");
return -1;
}
//调用avformat_find_stream_info函数查找流信息==注意传入的参数
if(avformat_find_stream_info(pFormatCtx,NULL)<0){
printf("Couldn't find stream information.\n");
return -1;
}
//此索引的功能是什么？猜测：指明视频流的索引
//在一个文件中，音频流和视频流是两个流
videoindex=-1;
for(i=0; i<pFormatCtx->nb_streams; i++)//遍历流并查找视频流信息
if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
videoindex=i;
break;
}
//当视频流索引为-1时，可以认为视频流不存在
if(videoindex==-1){
printf("Didn't find a video stream.\n");
return -1;
}
//可以理解为codec与编码器信息相关
pCodecCtx=pFormatCtx->streams[videoindex]->codec;
pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec==NULL){
printf("Codec not found.\n");
return -1;
}
//调用avcodec_open2函数打开解码器
if(avcodec_open2(pCodecCtx, pCodec,NULL)<0){
printf("Could not open codec.\n");
return -1;
}
//alloc相关函数作用是分配内存==创建结构体
pFrame=av_frame_alloc();
pFrameYUV=av_frame_alloc();
//这几个函数的传入参数较多
//av_image_get_buffer_size函数用于计算buffer size 单位是byte
//av_malloc用于分配空间
out_buffer=(unsigned char *)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height,1));
//av_image_fill_arrays函数分配缓冲区，并填充data和linesize
av_image_fill_arrays(pFrameYUV->data, pFrameYUV->linesize,out_buffer,
AV_PIX_FMT_YUV420P,pCodecCtx->width, pCodecCtx->height,1);
//给packet分配空间
packet=(AVPacket *)av_malloc(sizeof(AVPacket));
//Output Info-----------------------------
printf("--------------- File Information ----------------\n");
//调用av_dump_format函数进行文件信息的输出
av_dump_format(pFormatCtx,0,filepath,0);
printf("-------------------------------------------------\n");
//sws_getContext分配并返回sws_Context结构体
img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
#if OUTPUT_YUV420P
fp_yuv=fopen("output.yuv","wb+");
#endif
//SDL初始化
if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
printf( "Could not initialize SDL - %s\n", SDL_GetError());
return -1;
}
//获取宽和高
screen_w = pCodecCtx->width;
screen_h = pCodecCtx->height;
//SDL 2.0 Support for multiple windows
screen = SDL_CreateWindow("Simplest ffmpeg player's Window", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
screen_w, screen_h,
SDL_WINDOW_OPENGL);
//错误处理
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;
//SDL End----------------------
//遍历读取视频的每一帧
while(av_read_frame(pFormatCtx, packet)>=0){
if(packet->stream_index==videoindex){
//解码
ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
if(ret < 0){
printf("Decode Error.\n");
return -1;
}
if(got_picture){
//调用sws_scale函数进行缩放操作
sws_scale(img_convert_ctx, (const unsigned char* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
pFrameYUV->data, pFrameYUV->linesize);
#if OUTPUT_YUV420P
//y_size是尺寸=宽x高
y_size=pCodecCtx->width*pCodecCtx->height;
//分别将Y U V数据写入fp_yuv
fwrite(pFrameYUV->data[0],1,y_size,fp_yuv); //Y
fwrite(pFrameYUV->data[1],1,y_size/4,fp_yuv); //U
fwrite(pFrameYUV->data[2],1,y_size/4,fp_yuv); //V
#endif
//SDL---------------------------
#if 0
SDL_UpdateTexture( sdlTexture, NULL, pFrameYUV->data[0], pFrameYUV->linesize[0] );
#else
//更新纹理？
SDL_UpdateYUVTexture(sdlTexture, &sdlRect,
pFrameYUV->data[0], pFrameYUV->linesize[0],
pFrameYUV->data[1], pFrameYUV->linesize[1],
pFrameYUV->data[2], pFrameYUV->linesize[2]);
#endif
SDL_RenderClear( sdlRenderer );
SDL_RenderCopy( sdlRenderer, sdlTexture, NULL, &sdlRect);
SDL_RenderPresent( sdlRenderer );
//SDL End-----------------------
//Delay 40ms
SDL_Delay(40);
}
}
av_free_packet(packet);
}
//flush decoder冲刷解码器
//FIX: Flush Frames remained in Codec
while (1) {
//这个地方的冲刷实现：直接进行解码，然后对解码返回的ret进行判断
//相比于上一个while，这里不再对av_read_frame返回值进行判断，而是选择默认解码
//通过解码得到的值来判断是否冲刷干净
ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
if (ret < 0)
break;
if (!got_picture)
break;
sws_scale(img_convert_ctx, (const unsigned char* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
pFrameYUV->data, pFrameYUV->linesize);
#if OUTPUT_YUV420P
int y_size=pCodecCtx->width*pCodecCtx->height;
fwrite(pFrameYUV->data[0],1,y_size,fp_yuv); //Y
fwrite(pFrameYUV->data[1],1,y_size/4,fp_yuv); //U
fwrite(pFrameYUV->data[2],1,y_size/4,fp_yuv); //V
#endif
//SDL---------------------------
SDL_UpdateTexture( sdlTexture, &sdlRect, pFrameYUV->data[0], pFrameYUV->linesize[0] );
SDL_RenderClear( sdlRenderer );
SDL_RenderCopy( sdlRenderer, sdlTexture, NULL, &sdlRect);
SDL_RenderPresent( sdlRenderer );
//SDL End-----------------------
//Delay 40ms
SDL_Delay(40);
}
sws_freeContext(img_convert_ctx);
#if OUTPUT_YUV420P
//关闭文件
fclose(fp_yuv);
#endif
//退出SDL
SDL_Quit();
//清理
av_frame_free(&pFrameYUV);
av_frame_free(&pFrame);
avcodec_close(pCodecCtx);
//关闭输入流
avformat_close_input(&pFormatCtx);
return 0;
}
