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   源码介绍

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视频转换生成的图片保存在如下目录：

    

#include "ffmpeg.h"

AVFormatContext * m_in_format_ctx = NULL;
int video_stream_idx = -1; 

void initialize_all()
{
	av_register_all();
	avformat_network_init();
}

int init_input(char * filename,AVFormatContext ** in_format_ctx)
{
	int ret = 0;
	ret = avformat_open_input(in_format_ctx, filename,NULL, NULL);
	if (ret != 0)
	{
		printf("Call avformat_open_input function failed!\n");
		return 0;
	}
	if (av_find_stream_info(*in_format_ctx) < 0)
	{
		printf("Call av_find_stream_info function failed!\n");
		return 0;
	}

	ret = open_codec_context(&video_stream_idx, in_format_ctx, AVMEDIA_TYPE_VIDEO);
	if (ret != 1)
	{
		printf("Call open_codec_context function failed!\n");
		return 0;
	}

	//The output of input information
	av_dump_format(*in_format_ctx, -1, filename, 0);

	return 1;
}

int open_codec_context(int *stream_idx, AVFormatContext ** in_format_ctx, enum AVMediaType type)
{
	int ret = 0;
	AVStream * st = NULL;
	AVCodecContext * dec_ctx = NULL;
	AVCodec * dec = NULL;

	ret = av_find_best_stream((*in_format_ctx), type, -1, -1, NULL, 0);
	if (ret < 0) 
	{
		printf("Call av_find_best_stream function failed!\n");
		return 0;
	} 
	else
	{
		*stream_idx = ret;
		st = (*in_format_ctx)->streams[*stream_idx];

		/* find decoder for the stream */
		dec_ctx = st->codec;
		dec = avcodec_find_decoder(dec_ctx->codec_id);
		if (!dec) 
		{
			return AVERROR(EINVAL);
		}

		if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0)
		{
			printf("Call avcodec_open2 function failed!\n");
			return 0;
		}
	}
	return 1;
}

void uinit_input(AVFormatContext * in_format_ctx)
{
	avcodec_close(in_format_ctx->streams[video_stream_idx]->codec);
	avformat_close_input(&in_format_ctx);
	av_free(in_format_ctx);
}

int read_frame(AVFormatContext * in_format,char * filepath)
{
	int ret = 0;
	AVPacket pkt_in;
	AVPacket pkt_out;  
	AVFrame * picture = av_frame_alloc();
	int got_picture_ptr = 0;
	AVFormatContext* pFormatCtx = NULL;   
	AVStream* video_st = NULL;  
	AVCodecContext* pCodecCtx = NULL;  
	AVCodec* pCodec = NULL;  
	FILE * video_dst_file = NULL;
	char file_name[50] = {0};

	/* find the mpeg1 video encoder */
	pCodec = avcodec_find_encoder(AV_CODEC_ID_MJPEG);
	if (!pCodec) 
	{
		printf("Call avcodec_find_encoder function failed!\n");
		return 0;
	}

	pCodecCtx = avcodec_alloc_context3(pCodec);
	if (!pCodecCtx) 
	{
		printf("Call avcodec_alloc_context3 function failed!\n");
		return 0;
	}


	pCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;  
	pCodecCtx->pix_fmt = AV_PIX_FMT_YUVJ420P;  

	//If you want to change the image size can do the zoom function
	pCodecCtx->width = in_format->streams[video_stream_idx]->codec->width;    
	pCodecCtx->height = in_format->streams[video_stream_idx]->codec->height;  

	pCodecCtx->time_base.num = 1;    
	pCodecCtx->time_base.den = 15;     
	//Output some information  

	if (avcodec_open2(pCodecCtx, pCodec,NULL) < 0)
	{  
		printf("Could not open codec.\n");  
		return 0; 
	}  

	av_init_packet(&pkt_in);
	av_init_packet(&pkt_out);

	//return 0 if OK, < 0 on error or end of file
	while (av_read_frame(in_format, &pkt_in) == 0)
	{
		//video && key frame
		if (pkt_in.stream_index == video_stream_idx && pkt_in.flags == 1)
		{
			ret = avcodec_decode_video2(in_format->streams[video_stream_idx]->codec, picture, &got_picture_ptr, &pkt_in);  
			//success decode
			if(got_picture_ptr)
			{ 
				av_new_packet(&pkt_out,pCodecCtx->width * pCodecCtx->height * 3);
				//encode  
				ret = avcodec_encode_video2(pCodecCtx, &pkt_out,picture, &got_picture_ptr);  
				if(ret < 0)
				{  
					printf("Encode Error.\n");  
					avcodec_close(pCodecCtx);
					av_free(pCodecCtx);
					av_free_packet(&pkt_out);
					return 0;  
				}  
				//success encode
				if (got_picture_ptr)
				{  
					generate_file_name(file_name,filepath,pkt_in.pts);

					//Method 1
					//save_picture_init(&pFormatCtx,video_st,pCodecCtx,file_name);
					//save_picture_uinit_2(pFormatCtx,pkt_out);
					//Method 2
					save_picture_init_2(&video_dst_file,file_name);
					if(video_dst_file)
					{
						save_picture_uinit(video_dst_file,pkt_out);
					}
				} 
			}
		}
		av_free_packet(&pkt_in);
	}
	av_frame_free(&picture);
	avcodec_close(pCodecCtx);
	av_free(pCodecCtx);

	return 1;
}

int  save_picture_init(AVFormatContext** out_format_ctx,AVStream * video_st,AVCodecContext* pCodecCtx,char * filename)
{	
	AVOutputFormat* fmt = NULL; 

	avformat_alloc_output_context2(out_format_ctx, NULL, NULL, filename);  
	fmt = (*out_format_ctx)->oformat;  

	video_st = avformat_new_stream((*out_format_ctx), 0);  
	if (video_st == NULL)
	{  
		return 0;  
	}  
	/*pCodecCtx = video_st->codec;  
	pCodecCtx->codec_id = fmt->video_codec; */ 
	av_dump_format((*out_format_ctx), 0, filename, 1);  

	if (avformat_write_header((*out_format_ctx), NULL))
	{
		printf("Call avformat_write_header function failed.\n");
		return 0 ;
	}
	return 1;
}

int  save_picture_init_2(FILE ** pFile,char * filename)
{
	*pFile = fopen(filename, "wb");
	return 1;
}

void  save_picture_uinit(FILE * pFile,AVPacket pkt)
{
	fwrite(pkt.data, sizeof(uint8_t),pkt.size, pFile);
	fclose(pFile);
	av_free_packet(&pkt);
}

void  save_picture_uinit_2(AVFormatContext* out_format_ct,AVPacket pkt)
{
	int ret = 0;

	//pkt.stream_index = video_st->index;  
	ret = av_interleaved_write_frame(out_format_ct, &pkt);
	if (ret != 0)
	{
		printf("error av_interleaved_write_frame _ video\n");
		return ;
	} 
	//Write Trailer  
	ret = av_write_trailer(out_format_ct);
	if (ret != 0)
	{
		printf("error av_interleaved_write_frame _ video\n");
	}
	av_free(out_format_ct);
}

void generate_file_name(char * file_name,char * file_path,long long pts)
{
	if (file_path[strlen(file_path) - 1] == '/')
	{
		sprintf(file_name,"%s%lld.jpg",file_path,pts);
	}
	else
	{
		sprintf(file_name,"%s/%lld.jpg",file_path,pts);
	}
}