AVFormatContext封装层：理论与实战（二）https://developer.aliyun.com/article/1473935
2、示例源码
以下源码实现下面命令同样的功能
ffmepg -i test.mp4 -c copy -f test.flv • 1
#include <libavutil/timestamp.h> #include <libavformat/avformat.h> static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt, const char *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(int argc, char **argv) { AVOutputFormat *ofmt = NULL; AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL; AVPacket pkt; const char *in_filename, *out_filename; int ret, i; int stream_index = 0; int *stream_mapping = NULL; int stream_mapping_size = 0; in_filename = "./debug/test.mp4"; out_filename = "./debug/test.flv"; if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) { fprintf(stderr, "Could not open input file '%s'", in_filename); goto end; } if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) { fprintf(stderr, "Failed to retrieve input stream information"); goto end; } printf("\n\n-------av_dump_format:ifmt_ctx----------------\n"); 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; goto end; } stream_mapping_size = ifmt_ctx->nb_streams; stream_mapping = av_mallocz_array(stream_mapping_size, sizeof(*stream_mapping)); if (!stream_mapping) { ret = AVERROR(ENOMEM); goto end; } 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 allocating output stream\n"); ret = AVERROR_UNKNOWN; goto end; } ret = avcodec_parameters_copy(out_stream->codecpar, in_codecpar); if (ret < 0) { fprintf(stderr, "Failed to copy codec parameters\n"); goto end; } out_stream->codecpar->codec_tag = 0; } printf("\n\n-------av_dump_format:ofmt_ctx----------------\n"); av_dump_format(ofmt_ctx, 0, out_filename, 1); if (!(ofmt->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); goto end; } } ret = avformat_write_header(ofmt_ctx, NULL); if (ret < 0) { fprintf(stderr, "Error occurred when opening output file\n"); goto end; } while (1) { AVStream *in_stream, *out_stream; /// 读取音视频压缩包 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) { av_packet_unref(&pkt); 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"); /// 交织写音视频包 ret = av_interleaved_write_frame(ofmt_ctx, &pkt); if (ret < 0) { fprintf(stderr, "Error muxing packet\n"); break; } av_packet_unref(&pkt);//包需要解引用 } av_write_trailer(ofmt_ctx); end: avformat_close_input(&ifmt_ctx); /* close output */ 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; }
3、运行结果
-------av_dump_format:ifmt_ctx---------------- -------av_dump_format:ofmt_ctx---------------- in: pts:0 pts_time:0 dts:0 dts_time:0 duration:1024 duration_time:0.0213333 stream_index:1 out: pts:0 pts_time:0 dts:0 dts_time:0 duration:21 duration_time:0.021 stream_index:1 in: pts:0 pts_time:0 dts:0 dts_time:0 duration:512 duration_time:0.04 stream_index:0 out: pts:0 pts_time:0 dts:0 dts_time:0 duration:40 duration_time:0.04 stream_index:0 in: pts:1024 pts_time:0.0213333 dts:1024 dts_time:0.0213333 duration:1024 duration_time:0.0213333 stream_index:1 out: pts:21 pts_time:0.021 dts:21 dts_time:0.021 duration:21 duration_time:0.021 stream_index:1 .... in: pts:1500672 pts_time:117.24 dts:1500672 dts_time:117.24 duration:512 duration_time:0.04 stream_index:0 out: pts:117240 pts_time:117.24 dts:117240 dts_time:117.24 duration:40 duration_time:0.04 stream_index:0 in: pts:5628928 pts_time:117.269 dts:5628928 dts_time:117.269 duration:1024 duration_time:0.0213333 stream_index:1 out: pts:117269 pts_time:117.269 dts:117269 dts_time:117.269 duration:21 duration_time:0.021 stream_index:1 in: pts:5629952 pts_time:117.291 dts:5629952 dts_time:117.291 duration:1024 duration_time:0.0213333 stream_index:1 out: pts:117291 pts_time:117.291 dts:117291 dts_time:117.291 duration:21 duration_time:0.021 stream_index:1 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './debug/test.mp4': Metadata: major_brand : isom minor_version : 512 compatible_brands: isomiso2avc1mp41 creation_time : 1970-01-01T00:00:00.000000Z encoder : Lavf53.24.2 Duration: 00:01:57.31, start: 0.000000, bitrate: 1436 kb/s Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1048 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default) Metadata: creation_time : 1970-01-01T00:00:00.000000Z handler_name : VideoHandler Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 383 kb/s (default) Metadata: creation_time : 1970-01-01T00:00:00.000000Z handler_name : SoundHandler Output #0, flv, to './debug/test.flv': Stream #0:0: Video: h264 (Main), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 1048 kb/s Stream #0:1: Audio: aac (LC), 48000 Hz, 5.1, fltp, 383 kb/s
使用 MediaInfo 查看未进行转封装前 test.mp4 的封装格式为 MPEG-4
使用 MediaInfo 查看转封装后新生成的 test.flv 文件的封装格式为 Flash Video
