FFMPEG学习----使用SDL构建视频播放器

#include <stdio.h>
#include <string.h>

extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libavutil/imgutils.h"
#include "SDL.h"
};
//依赖库
#pragma comment(lib, "avcodec.lib")
#pragma comment(lib, "avformat.lib")
#pragma comment(lib, "swscale.lib")
#pragma comment(lib, "avutil.lib")
#pragma comment(lib, "SDL2.lib")
#pragma comment(lib, "SDL2main.lib")

//Refresh Event
#define REFRESH_EVENT	(SDL_USEREVENT + 1)
//Break Event
#define BREAK_EVENT		(SDL_USEREVENT + 2)

bool thread_exit = false;
bool thread_pause = false;

int RefreshVideo(void *opaque)
{
	thread_exit = false;
	thread_pause = false;
	while (!thread_exit)
	{
		//没按 space
		if (!thread_pause)
		{
			SDL_Event event;
			event.type = REFRESH_EVENT;
			SDL_PushEvent(&event);
		}
		SDL_Delay(40);
	}
	thread_exit = false;
	thread_pause = false;
	//Break 退出main函数循环
	SDL_Event event;
	event.type = BREAK_EVENT;
	SDL_PushEvent(&event);
	return 0;
}

int main(int argc, char* argv[])
{
	//------------FFmpeg---------------- 
	AVFormatContext		*pFormatCtx = NULL;
	AVCodecContext		*pCodecCtx = NULL;
	AVCodec				*pCodec = NULL;
	AVFrame				*pFrame = NULL, *pFrameYUV = NULL;
	unsigned char		*out_buffer = NULL;
	AVPacket			packet;
	struct SwsContext	*img_convert_ctx = NULL;
	int					y_size;
	int					got_picture;
	int					i, videoIndex;
	int					frame_cnt = 1;

	//------------SDL---------------- 
	SDL_Window			*sdlScreen = NULL;
	SDL_Renderer		*sdlRenderer = NULL;
	SDL_Texture			*sdlTexture = NULL;
	SDL_Rect			sdlRect;
	SDL_Thread			*sdlThread = NULL;
	SDL_Event			event;


	char filepath[1024] = "";
	printf("Usage: program.exe Titanic.ts
");
	if (argc == 2)
	{
		strcpy(filepath, argv[1]);
	}
	else
	{
		printf("Could not find a file
");
		return -1;
	}


	av_register_all();

	if (avformat_open_input(&pFormatCtx, filepath, NULL, NULL) != 0)
	{
		printf("Couldn't open an input stream.
");
		return -1;
	}
	if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
	{
		printf("Couldn't find stream information.
");
		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("Couldn't find a video stream.
");
		return -1;
	}

	pCodecCtx = pFormatCtx->streams[videoIndex]->codec;
	pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
	if (pCodec == NULL)
	{
		printf("Codec not found.
");
		return -1;
	}
	if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
	{
		printf("Could not open codec.
");
		return -1;
	}

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

	pFrame = av_frame_alloc();
	pFrameYUV = av_frame_alloc();
	if (pFrame == NULL || pFrameYUV == NULL)
	{
		printf("memory allocation error
");
		return -1;
	}
	out_buffer = (unsigned char *)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height, 1));
	av_image_fill_arrays(pFrameYUV->data, pFrameYUV->linesize, out_buffer,
		AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height, 1);
	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 (SDL_Init(SDL_INIT_VIDEO))
	{
		printf("Could not initialize SDL - %s
", SDL_GetError());
		return -1;
	}


	sdlScreen = SDL_CreateWindow("FFmpeg Player", 
		SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
		pCodecCtx->width, pCodecCtx->height, SDL_WINDOW_OPENGL);
	if (sdlScreen == 0)
	{
		printf("SDL: could not create SDL_Window - exiting:%s
", SDL_GetError());
		return -1;
	}

	sdlRenderer = SDL_CreateRenderer(sdlScreen, -1, SDL_RENDERER_ACCELERATED);
	if (sdlRenderer == NULL)
	{
		printf("SDL: could not create SDL_Renderer - exiting:%s
", SDL_GetError());
		return -1;
	}

	sdlTexture = SDL_CreateTexture(sdlRenderer, SDL_PIXELFORMAT_IYUV, SDL_TEXTUREACCESS_STREAMING, pCodecCtx->width, pCodecCtx->height);
	if (sdlTexture == NULL)
	{
		printf("SDL: could not create SDL_Texture - exiting:%s
", SDL_GetError());
		return -1;
	}

	//设置图像显示位置
	sdlRect.x = 10;
	sdlRect.y = 10;
	sdlRect.w = pCodecCtx->width - 20;
	sdlRect.h = pCodecCtx->height - 20;

	sdlThread = SDL_CreateThread(RefreshVideo, NULL, NULL);

	while (true)
	{
		SDL_WaitEvent(&event);
		if (event.type == REFRESH_EVENT)
		{
			while (true)
			{
				if (av_read_frame(pFormatCtx, &packet) < 0)
				{
					thread_exit = true;
				}
				if (packet.stream_index == videoIndex)
				{
					break;
				}
			}
			if (avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, &packet) < 0)
			{
				printf("Decode Error.
");
				return -1;
			}
			if (got_picture)
			{
				sws_scale(img_convert_ctx, (const unsigned char* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
					pFrameYUV->data, pFrameYUV->linesize);

				SDL_UpdateYUVTexture(sdlTexture, NULL,
					pFrameYUV->data[0], pFrameYUV->linesize[0],
					pFrameYUV->data[1], pFrameYUV->linesize[1],
					pFrameYUV->data[2], pFrameYUV->linesize[2]
					);
				//SDL_UpdateTexture(sdlTexture, NULL, pFrameYUV->data[0], pFrameYUV->linesize[0]);
				SDL_RenderClear(sdlRenderer); 
				SDL_RenderCopy(sdlRenderer, sdlTexture, NULL, &sdlRect);
				SDL_RenderPresent(sdlRenderer);

				printf("Succeed to decode %d frame!
", frame_cnt);
				frame_cnt++;
			}
			av_free_packet(&packet);
		}
		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 = true;
		}
		else if (event.type == BREAK_EVENT)
		{
			break;
		}
	}//while

	SDL_Quit();

	sws_freeContext(img_convert_ctx);
	av_frame_free(&pFrameYUV);
	av_frame_free(&pFrame);
	avcodec_close(pCodecCtx);
	avformat_close_input(&pFormatCtx);

	return 0;
}

有人会疑惑，为什么解码后的pFrame不直接用于显示，而是调用swscale()转换之后进行显示？

如果不进行转换，而是直接调用SDL进行显示的话，会发现显示出来的图像是混乱的。关键问题在于解码后的pFrame的linesize里存储的不是图像的宽度，而是比宽度大一些的一个值。其原因目前还没有仔细调查（大概是出于性能的考虑）。例如分辨率为480x272的图像，解码后的视频的linesize[0]为512，而不是480。以第1行亮度像素（pFrame->data[0]）为例，从0-480存储的是亮度数据，而从480-512则存储的是无效的数据。因此需要使用swscale()进行转换。转换后去除了无效数据，linesize[0]变为480。就可以正常显示了。