ffmpeg 封装格式转换 MP4转AVI

av_register_all();

avformat_open_input()
avformat_find_stream_info()

//为输出格式分配AVFormatContext
avformat_alloc_output_context2()
//【关键步骤】 copy输入文件的设置到输出文件
avcodec_copy_context()

//打开输出文件
avio_open()

//将文件流头部数据写入文件
avformat_write_header()
//读取帧
av_read_frame()

//数据包写入文件
av_interleaved_write_frame()
//将文件流尾部数据写入文件并释放文件资源
av_write_trailer()

#include <stdio.h>
#include "stdafx.h"


extern "C"
{
#include <libavformat/avformat.h>
};


void log_ss(const char * msg, int d = -1123) {
	if (d == -1123) {
		printf_s("%s\n", msg);
	}
	else {
		printf_s("%s  %d \n", msg, d);
	}
}

int main()
{
    AVOutputFormat *ofmt = NULL;
    //Input AVFormatContext and Output AVFormatContext
    AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
    AVPacket pkt;
    int ret, i;
    int frame_index=0;
	const char * in_filename  = "F:/视频资源/gxsp.mp4";//Input file URL
	const char *  out_filename = "F:/视频资源/gxsp.avi";//Output file URL


	//1. 注册初始化
	//H.264 bitstream malformed, no startcode found, use the video bitstream filte错误解决方法   第一步
	AVBitStreamFilterContext *filter = av_bitstream_filter_init("h264_mp4toannexb");
	if (NULL == filter)
	{
		log_ss("filter init fail");
	}
	//av_register_bitstream_filter(filter->filter);
    av_register_all();
	//2. 打开媒体文件与AVFormatContext关联
    //Input
    if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
		log_ss( "Could not open input file.");
        goto end;
    }
	//3. 获取视频流信息
    if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {//
		log_ss( "Failed to retrieve input stream information");
        goto end;
    }
	log_ss("--------------- In File Information ----------------");
    av_dump_format(ifmt_ctx, 0, in_filename, 0);
	log_ss("--------------- In File Information ----------------");
    //4. 初始化输出视频码流的AVFormatContext，与输出文件相关联
    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
    if (!ofmt_ctx) {
		log_ss( "Could not create output context");
        ret = AVERROR_UNKNOWN;
        goto end;
    }

	//获取AVOutputFormat
    ofmt = ofmt_ctx->oformat;
    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        //Create output AVStream according to input AVStream
        AVStream *in_stream = ifmt_ctx->streams[i];
        AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);// 初始化AVStream 
        if (!out_stream) {
			log_ss( "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }
		//5.【关键步骤】 copy输入文件的设置到输出文件
		  if (avcodec_copy_context(out_stream->codec, in_stream->codec) < 0) {
				log_ss( "Failed to copy context from input to output stream codec context\n");
			  goto end;
		   }
        out_stream->codec->codec_tag = 0;
        if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
            out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
    }
	log_ss("--------------- Out File Information ----------------");
    av_dump_format(ofmt_ctx, 0, out_filename, 1);
	log_ss("--------------- Out File Information ----------------");
	//6. 打开输出文件。
    if (!(ofmt->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
			log_ss( "Could not open output file");
			log_ss(  out_filename);
            goto end;
        }
    }
    //7. 写入头部到文件
    if (avformat_write_header(ofmt_ctx, NULL) < 0) {
		log_ss( "Error occurred when opening output file\n");
        goto end;
    }
	
	//8. 写入数据到文件
    while (1) {
        AVStream *in_stream, *out_stream;
        //Get an AVPacket
        ret = av_read_frame(ifmt_ctx, &pkt);
        if (ret < 0)
            break;
        in_stream  = ifmt_ctx->streams[pkt.stream_index];
        out_stream = ofmt_ctx->streams[pkt.stream_index];

		//H.264 bitstream malformed, no startcode found, use the video bitstream filte错误解决方法   第二步
		if (pkt.stream_index == 0) {
			AVPacket fpkt = pkt;
			int a = av_bitstream_filter_filter(filter,
				out_stream->codec, NULL, &fpkt.data, &fpkt.size,
				pkt.data, pkt.size, pkt.flags & AV_PKT_FLAG_KEY);
			pkt.data = fpkt.data;
			pkt.size = fpkt.size;
		}

        //Convert PTS/DTS
        pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
        pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
        pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
        pkt.pos = -1;
		//将AVPacket（存储视频压缩码流数据）写入文件   av_interleaved_write_frame将对 packet 进行缓存和 pts 检查，av_write_frame没有
        if (av_interleaved_write_frame(ofmt_ctx, &pkt) < 0) {
			log_ss( "Error muxing packets");
            break;
        }
        log_ss("Write frames to output file:",frame_index);
		av_packet_unref(&pkt);
        frame_index++;
    }

	//9. 写入文件尾部 
    //Write file trailer
    av_write_trailer(ofmt_ctx);
end:
    avformat_close_input(&ifmt_ctx);
    /* close output */
    if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
        avio_close(ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);

	getchar();
    return 0;
}

AVBitStreamFilterContext *filter = av_bitstream_filter_init("h264_mp4toannexb");
    if (NULL == filter)
    {
        cout<<"filter init fail"<<endl;
    }
    av_register_bitstream_filter(filter->filter);

if (pkt.stream_index == 0) {
			AVPacket fpkt = pkt;
			int a = av_bitstream_filter_filter(filter,
				out_stream->codec, NULL, &fpkt.data, &fpkt.size,
				pkt.data, pkt.size, pkt.flags & AV_PKT_FLAG_KEY);
			pkt.data = fpkt.data;
			pkt.size = fpkt.size;
		}