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;
}