准备
ffmepeg 4.4
一段H264的视频文件
一段acc格式的音频文件
封装流程
1.使用avformat_open_input分别打开视频和音频文件，初始化其AVFormatContext，使用avformat_find_stream_info获取编码器基本信息
2.使用avformat_alloc_output_context2初始化输出的AVFormatContext结构
3.使用函数avformat_new_stream给输出的AVFormatContext结构创建音频和视频流，使用avcodec_parameters_copy方法将音视频的编码参数拷贝到新创建的对应的流的codecpar结构中
4.使用avio_open打开输出文件，初始化输出AVFormatContext结构中的IO上下文结构
5.使用avformat_write_header写入流的头信息到输出文件中
6.根据时间戳同步原则交错写入音视频数据，并对时间戳信息进行设置和校准
7.写入流预告信息到输出文件中（moov）
8.释放空间，关闭文件
源码
#include <stdio.h>
#define __STDC_CONSTANT_MACROS
#ifdef _WIN32
//Windows
extern "C"
{
#include "libavformat/avformat.h"
};
#else
//Linux...
#ifdef __cplusplus
extern "C"
{
#endif
#include <libavformat/avformat.h>
#ifdef __cplusplus
};
#endif
#endif
int main(int argc, char* argv[]) {
AVOutputFormat* ofmt = NULL;
//Input AVFormatContext and Output AVFormatContext
AVFormatContext* ifmt_ctx_v = NULL, * ifmt_ctx_a = NULL, * ofmt_ctx = NULL;
AVPacket pkt;
int ret, i;
int videoindex_v = -1, videoindex_out = -1;
int audioindex_a = -1, audioindex_out = -1;
int frame_index = 0;
int64_t cur_pts_v = 0, cur_pts_a = 0;
int writing_v = 1, writing_a = 1;
const char* in_filename_v = "D:/测试工程/sound/ffmpeg_demo.h264";
const char* in_filename_a = "D:/测试工程/sound/ffmpeg_demo.aac";
const char* out_filename = "D:/测试工程/sound/muxing.mp4";//Output file URL
if ((ret = avformat_open_input(&ifmt_ctx_v, in_filename_v, 0, 0)) < 0) {
printf("Could not open input file.");
goto end;
}
if ((ret = avformat_find_stream_info(ifmt_ctx_v, 0)) < 0) {
printf("Failed to retrieve input stream information");
goto end;
}
if ((ret = avformat_open_input(&ifmt_ctx_a, in_filename_a, 0, 0)) < 0) {
printf("Could not open input file.");
goto end;
}
if ((ret = avformat_find_stream_info(ifmt_ctx_a, 0)) < 0) {
printf("Failed to retrieve input stream information");
goto end;
}
//Output
avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
if (!ofmt_ctx) {
printf("Could not create output context\n");
ret = AVERROR_UNKNOWN;
goto end;
}
ofmt = ofmt_ctx->oformat;
for (i = 0; i < ifmt_ctx_v->nb_streams; i++) {
//Create output AVStream according to input AVStream
if (ifmt_ctx_v->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
AVStream* out_stream = avformat_new_stream(ofmt_ctx, nullptr);
videoindex_v = i;
if (!out_stream) {
printf("Failed allocating output stream\n");
ret = AVERROR_UNKNOWN;
goto end;
}
videoindex_out = out_stream->index;
//Copy the settings of AVCodecContext
if (avcodec_parameters_copy(out_stream->codecpar, ifmt_ctx_v->streams[i]->codecpar) < 0) {
printf("Failed to copy context from input to output stream codec context\n");
goto end;
}
break;
}
}
for (i = 0; i < ifmt_ctx_a->nb_streams; i++) {
//Create output AVStream according to input AVStream
if (ifmt_ctx_a->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
AVStream* out_stream = avformat_new_stream(ofmt_ctx, nullptr);
audioindex_a = i;
if (!out_stream) {
printf("Failed allocating output stream\n");
ret = AVERROR_UNKNOWN;
goto end;
}
audioindex_out = out_stream->index;
//Copy the settings of AVCodecContext
if (avcodec_parameters_copy(out_stream->codecpar, ifmt_ctx_a->streams[i]->codecpar) < 0) {
printf("Failed to copy context from input to output stream codec context\n");
goto end;
}
out_stream->codecpar->codec_tag = 0;
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
ofmt_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
break;
}
}
/* open the output file, if needed */
if (!(ofmt->flags & AVFMT_NOFILE)) {
if (avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE)) {
fprintf(stderr, "Could not open '%s': %d\n", out_filename,
ret);
goto end;
}
}
//Write file header
if (avformat_write_header(ofmt_ctx, NULL) < 0) {
fprintf(stderr, "Error occurred when opening output file: %d\n",
ret);
goto end;
}
//写入数据
while (writing_v || writing_a)
{
AVFormatContext* ifmt_ctx;
int stream_index = 0;
AVStream* in_stream, * out_stream;
if (writing_v &&
(!writing_a || av_compare_ts(cur_pts_v, ifmt_ctx_v->streams[videoindex_v]->time_base,
cur_pts_a, ifmt_ctx_a->streams[audioindex_a]->time_base) <= 0))
{
ifmt_ctx = ifmt_ctx_v;
stream_index = videoindex_out;
if (av_read_frame(ifmt_ctx, &pkt) >= 0)
{
do {
in_stream = ifmt_ctx->streams[pkt.stream_index];
out_stream = ofmt_ctx->streams[stream_index];
if (pkt.stream_index == videoindex_v)
{
//FIX：No PTS (Example: Raw H.264)
//Simple Write PTS
if (pkt.pts == AV_NOPTS_VALUE)
{
//Write PTS
AVRational time_base1 = in_stream->time_base;
//Duration between 2 frames (us)
int64_t calc_duration = (double)AV_TIME_BASE / av_q2d(in_stream->r_frame_rate);
//Parameters
pkt.pts = (double)(frame_index * calc_duration) / (double)(av_q2d(time_base1) * AV_TIME_BASE);
pkt.dts = pkt.pts;
pkt.duration = (double)calc_duration / (double)(av_q2d(time_base1) * AV_TIME_BASE);
frame_index++;
printf("frame_index: %d\n ", frame_index);
}
cur_pts_v = pkt.pts;
break;
}
} while
(av_read_frame(ifmt_ctx, &pkt) >= 0);
}
else
{
writing_v = 0;
continue;
}
}
else
{
ifmt_ctx = ifmt_ctx_a;
stream_index = audioindex_out;
if (av_read_frame(ifmt_ctx, &pkt) >= 0)
{
do {
in_stream = ifmt_ctx->streams[pkt.stream_index];
out_stream = ofmt_ctx->streams[stream_index];
if (pkt.stream_index == audioindex_a)
{
//FIX：No PTS
//Simple Write PTS
if (pkt.pts == AV_NOPTS_VALUE)
{
//Write PTS
AVRational time_base1 = in_stream->time_base;
//Duration between 2 frames (us)
int64_t calc_duration = (double)AV_TIME_BASE / av_q2d(in_stream->r_frame_rate);
//Parameters
pkt.pts = (double)(frame_index * calc_duration) /
(double)(av_q2d(time_base1) * AV_TIME_BASE);
pkt.dts = pkt.pts;
pkt.duration = (double)calc_duration / (double)(av_q2d(time_base1) * AV_TIME_BASE);
frame_index++;
}
cur_pts_a = pkt.pts;
break;
}
} while (av_read_frame(ifmt_ctx, &pkt) >= 0);
}
else
{
writing_a = 0;
continue;
}
}
//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;
pkt.stream_index = stream_index;
printf("Write 1 Packet. size:%5d\tpts:%lld\n", pkt.size, pkt.pts);
//Write
if (av_interleaved_write_frame(ofmt_ctx, &pkt) < 0) {
printf("Error muxing packet\n");
break;
}
av_packet_unref(&pkt);
}
printf("Write file trailer.\n");
//Write file trailer
av_write_trailer(ofmt_ctx);
end:
avformat_close_input(&ifmt_ctx_v);
avformat_close_input(&ifmt_ctx_a);
/* close output */
if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
avio_close(ofmt_ctx->pb);
avformat_free_context(ofmt_ctx);
if (ret < 0 && ret != AVERROR_EOF) {
printf("Error occurred.\n");
return -1;
}
return 0;
}小结
这里需要几个概念简单说明下：
tbr 表示每秒帧数
tbn 表示数据流的实际真实帧率的倒数
如：