avformat_alloc_output_context2() 生成输出文件的上下文
avformat_free_context() 释放输出上下文
avformat_new_stream() 创建新的stream/track
avcodec_parameters_copy() 创建stream之后 需要拷贝相应的参数 比如视频有sps和pps
avformat_write_header() 生成多媒体文件头
av_write_frame()/ av_interleaved_write_frame()[交叉存储数据] 写入数据
av_write_trailer() 写完多媒体文件之后，把多媒体文件的尾部信息写入。
时间基time_base pts和 dts的理解
https://blog.csdn.net/bixinwei22/article/details/78770090
https://blog.csdn.net/zhuweigangzwg/article/details/64919706
#include
#include
staticvoidlog_packet(constAVFormatContext *fmt_ctx,constAVPacket *pkt,constchar*tag)
{
AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;
printf("%s: pts:%s pts_time:%s, dts:%s, dts_time:%s duration:%s duration_time:%s, stream_index:%d\n",
tag, av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base), av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base), av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base), pkt->stream_index);
}
int main(intargc,char*argv[])
{
AVOutputFormat *ofmt =NULL;
AVFormatContext *ifmt_ctx =NULL, *ofmt_ctx =NULL;
AVPacket pkt;
constchar*in_filename, *out_filename;
intret, i;
intstream_index;
int*stream_mapping =NULL;
intstream_mapping_size =0;
if(argc <3) {
printf("usage: %s input output \n"
"API example program to remux a media file with libavformat and libavcodec.\n"
"The output format is guessed according to the file extension.\n"
"\n", argv[0]);
return 1;
}
in_filename = argv[1];
out_filename = argv[2];
av_register_all();
if((ret = avformat_open_input(&ifmt_ctx, in_filename,0,0)) <0) {
fprintf(stderr,"Could not open input file '%s'", in_filename);
gotoend;
}
if((ret = avformat_find_stream_info(ifmt_ctx,0)) <0) {
fprintf(stderr,"Falied to retrieve input stream information");
gotoend;
}
av_dump_format(ifmt_ctx,0, in_filename,0);
avformat_alloc_output_context2(&ofmt_ctx,NULL,NULL, out_filename);
if(!ofmt_ctx) {
fprintf(stderr,"Could not create output context\n");
ret = AVERROR_UNKNOWN;
gotoend;
}
stream_mapping_size = ifmt_ctx->nb_streams;
stream_mapping = av_mallocz_array(stream_mapping_size,sizeof(*stream_mapping));
if(!stream_mapping) {
ret = AVERROR(ENOMEM);
gotoend;
}
ofmt = ofmt_ctx->oformat;
for(i =0; i < ifmt_ctx->nb_streams; i++) {
AVStream *out_stream;
AVStream *in_stream = ifmt_ctx->streams[i];
AVCodecParameters *in_codecpar = in_stream->codecpar;
if(in_codecpar->codec_type != AVMEDIA_TYPE_AUDIO &&
in_codecpar->codec_type != AVMEDIA_TYPE_VIDEO &&
in_codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE) {
stream_mapping[i] = -1;
continue;
}
stream_mapping[i] = stream_index++;
out_stream = avformat_new_stream(ofmt_ctx,NULL);
if(!out_stream) {
fprintf(stderr,"Failed allocting output stream\n");
ret = AVERROR_UNKNOWN;
gotoend;
}
ret = avcodec_parameters_copy(out_stream->codecpar, in_codecpar);
if(ret <0) {
fprintf(stderr,"Failed to copy codec parameters\n");
gotoend;
}
out_stream->codecpar->codec_tag =0;
}
av_dump_format(ofmt_ctx,0, out_filename,1);
if(!(ofmt_ctx->flags & AVFMT_NOFILE)) {
ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
if(ret <0) {
fprintf(stderr,"Could not open output file '%s'", out_filename);
gotoend;
}
}
ret = avformat_write_header(ofmt_ctx,NULL);
if(ret <0) {
fprintf(stderr,"Error occurred when opening output file\n");
gotoend;
}
while(1) {
AVStream *in_stream, *out_stream;
ret = av_read_frame(ifmt_ctx, &pkt);
if(ret <0) {
break;
}
in_stream = ifmt_ctx->streams[pkt.stream_index];
if(pkt.stream_index >= stream_mapping_size || stream_mapping[pkt.stream_index] <0) {
continue;
}
pkt.stream_index = stream_mapping[pkt.stream_index];
out_stream = ofmt_ctx->streams[pkt.stream_index];
log_packet(ifmt_ctx, &pkt,"in");
/* copy packet */
pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, 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;
log_packet(ofmt_ctx, &pkt,"out");
ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
if(ret <0) {
fprintf(stderr,"Error muxing packet\n");
break;
}
av_packet_unref(&pkt);
}
av_write_trailer(ofmt_ctx);
end:
avformat_close_input(&ifmt_ctx);
if(ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE)) {
avio_closep(&ofmt_ctx->pb);
}
avformat_free_context(ofmt_ctx);
av_freep(&stream_mapping);
if(ret <0&& ret != AVERROR_EOF) {
fprintf(stderr,"Error occurred: %s\n", av_err2str(ret));
return 1;
}
return 0;
}
