本文主要实现使用最新版的ffmpeg生成模拟yuv数据和模拟音频数据再合成为mp4文件。重要代码都是来自官方，稳定性可靠。
本文程序的环境搭建参考我的第一篇FFMPEG教程：https://blog.csdn.net/zhangamxqun/article/details/80304494
不知道如何生成yuv帧数据？不知道如何生成音频数据? 不知道如何合成mp4文件？甚至不知道如何使用最新版的ffmpeg?编译不过，一堆错误，快要抓狂？
下面就是核心代码和最详细的注释：
/**
根据官方示例，实现FFMPEG4.0生成模拟mp4文件，作者自己测试正确可用
解决了windows下的编译问题，生成的结果文件为generated.mp4，因为码率设置的比较低，清晰度不是很高。
中文注释非常详细，涉及的知识点：yuv格式，aac格式，时间戳，时间基，帧率，重采样，编码，合成等等。信息量很大。
作者：明天继续
使用的ffmpeg版本：ffmpeg-20180508-293a6e8-win32
开发工具：vs2012
**/
#include "stdafx.h"
#include <Windows.h>
#include <wingdi.h>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <math.h>
#if _MSC_VER
#define snprintf sprintf_s //解决windows下编译问题
#define PRIx64 "I64x"
#define PRIX64 "I64X"
#define PRId64 "I64d"
#endif
#define __STDC_CONSTANT_MACROS //解决windows下编译问题
extern "C" {
#include <libavutil/avassert.h>
#include <libavutil/channel_layout.h>
#include <libavutil/opt.h>
#include <libavutil/mathematics.h>
#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
#include <libswresample/swresample.h>
}
//lib库的路径请按照自己的项目重新设置
#pragma comment(lib,"../../ffmpeg-20180508-293a6e8-win32-dev/lib/avcodec.lib")
#pragma comment(lib,"../../ffmpeg-20180508-293a6e8-win32-dev/lib/avformat.lib")
#pragma comment(lib,"../../ffmpeg-20180508-293a6e8-win32-dev/lib/avfilter.lib")
#pragma comment(lib,"../../ffmpeg-20180508-293a6e8-win32-dev/lib/avutil.lib")
#pragma comment(lib,"../../ffmpeg-20180508-293a6e8-win32-dev/lib/swscale.lib")
#pragma comment(lib,"../../ffmpeg-20180508-293a6e8-win32-dev/lib/swresample.lib")
#define STREAM_DURATION 10.0
#define STREAM_FRAME_RATE 25 /* 每秒25帧*/
#define STREAM_PIX_FMT AV_PIX_FMT_YUV420P /* 默认的像素格式 */
#define SCALE_FLAGS SWS_BICUBIC
char tempts[AV_TS_MAX_STRING_SIZE] = {0};
char temperro[AV_ERROR_MAX_STRING_SIZE]={0};
char * av_ts2str_f(int64_t ts)
{
return av_ts_make_string(tempts, ts);
}
char* av_ts2timestr_f(int64_t ts, AVRational *tb)
{
return av_ts_make_time_string(tempts, ts, tb);
}
char* av_err2str_f(int64_t errnum)
{
return av_make_error_string(temperro, AV_ERROR_MAX_STRING_SIZE, errnum);
}
// 单个输出流的包装器
typedef struct OutputStream {
AVStream *st;
AVCodecContext *enc;
/* 将要产生的下一帧的播放时间戳 */
int64_t next_pts;
int samples_count;
AVFrame *frame;
AVFrame *tmp_frame;
float t, tincr, tincr2;
struct SwsContext *sws_ctx;
struct SwrContext *swr_ctx;
} OutputStream;
static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt)
{
AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;
printf("pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",
av_ts2str_f(pkt->pts), av_ts2timestr_f(pkt->pts, time_base),
av_ts2str_f(pkt->dts), av_ts2timestr_f(pkt->dts, time_base),
av_ts2str_f(pkt->duration), av_ts2timestr_f(pkt->duration, time_base),
pkt->stream_index);
}
static int write_frame(AVFormatContext *fmt_ctx, const AVRational *time_base, AVStream *st, AVPacket *pkt)
{
/* 调节输出包的时间基，从编码器时间基到流时间基 */
av_packet_rescale_ts(pkt, *time_base, st->time_base);
pkt->stream_index = st->index;
/* 写入压缩后的帧到输出文件. */
log_packet(fmt_ctx, pkt);
return av_interleaved_write_frame(fmt_ctx, pkt);
}
//
///* 添加一个输出流. */
static void add_stream(OutputStream *ost, AVFormatContext *oc,
AVCodec **codec,
enum AVCodecID codec_id)
{
AVCodecContext *c;
int i;
/* 查找编码器 */
*codec = avcodec_find_encoder(codec_id);
if (!(*codec)) {
fprintf(stderr, "Could not find encoder for '%s'\n",
avcodec_get_name(codec_id));
exit(1);
}
ost->st = avformat_new_stream(oc, NULL);
if (!ost->st) {
fprintf(stderr, "Could not allocate stream\n");
exit(1);
}
ost->st->id = oc->nb_streams-1;
c = avcodec_alloc_context3(*codec);
if (!c) {
fprintf(stderr, "Could not alloc an encoding context\n");
exit(1);
}
ost->enc = c;
switch ((*codec)->type) {
case AVMEDIA_TYPE_AUDIO:
c->sample_fmt = (*codec)->sample_fmts ?
(*codec)->sample_fmts[0] : AV_SAMPLE_FMT_FLTP;
c->bit_rate = 64000;
c->sample_rate = 44100;
if ((*codec)->supported_samplerates) {
c->sample_rate = (*codec)->supported_samplerates[0];
for (i = 0; (*codec)->supported_samplerates[i]; i++) {
if ((*codec)->supported_samplerates[i] == 44100)
c->sample_rate = 44100;
}
}
c->channels = av_get_channel_layout_nb_channels(c->channel_layout);
c->channel_layout = AV_CH_LAYOUT_STEREO;
if ((*codec)->channel_layouts) {
c->channel_layout = (*codec)->channel_layouts[0];
for (i = 0; (*codec)->channel_layouts[i]; i++) {
if ((*codec)->channel_layouts[i] == AV_CH_LAYOUT_STEREO)
c->channel_layout = AV_CH_LAYOUT_STEREO;
}
}
c->channels = av_get_channel_layout_nb_channels(c->channel_layout);
ost->st->time_base.num = 1;
ost->st->time_base.den = c->sample_rate;
break;
case AVMEDIA_TYPE_VIDEO:
c->codec_id = codec_id;
c->bit_rate = 400000;
/* 设置要合成的视频源的分辨率 */
c->width = 1440;
c->height = 900;
/* 设置每一帧的展示时间（时间基）. 对于固定帧率，时间基就是帧率的倒数 */
ost->st->time_base.num = 1;
ost->st->time_base.den = STREAM_FRAME_RATE;
c->time_base = ost->st->time_base;
c->gop_size = 12; /*每12帧一个关键帧 */
c->pix_fmt = STREAM_PIX_FMT;
if (c->codec_id == AV_CODEC_ID_MPEG2VIDEO) {
/* 测试放入B 帧 */
c->max_b_frames = 2;
}
if (c->codec_id == AV_CODEC_ID_MPEG1VIDEO) {
/* 避免使用宏块.*/
c->mb_decision = 2;
}
break;
default:
break;
}
/* 一些格式流的头分开放置 */
if (oc->oformat->flags & AVFMT_GLOBALHEADER)
c->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
}
/**************************************************************/
/* 音频输出 */
static AVFrame *alloc_audio_frame(enum AVSampleFormat sample_fmt,
uint64_t channel_layout,
int sample_rate, int nb_samples)
{
AVFrame *frame = av_frame_alloc();
int ret;
if (!frame) {
fprintf(stderr, "Error allocating an audio frame\n");
exit(1);
}
frame->format = sample_fmt;
frame->channel_layout = channel_layout;
frame->sample_rate = sample_rate;
frame->nb_samples = nb_samples;
if (nb_samples) {
ret = av_frame_get_buffer(frame, 0);
if (ret < 0) {
fprintf(stderr, "Error allocating an audio buffer\n");
exit(1);
}
}
return frame;
}
static void open_audio(AVFormatContext *oc, AVCodec *codec, OutputStream *ost, AVDictionary *opt_arg)
{
AVCodecContext *c;
int nb_samples;
int ret;
AVDictionary *opt = NULL;
c = ost->enc;
/* 打开一片编码器 */
av_dict_copy(&opt, opt_arg, 0);
ret = avcodec_open2(c, codec, &opt);
av_dict_free(&opt);
if (ret < 0) {
fprintf(stderr, "Could not open audio codec: %s\n", av_err2str_f(ret));
exit(1);
}
/* 初始化信号生成器 */
ost->t = 0;
ost->tincr = 2 * M_PI * 110.0 / c->sample_rate;
/* 每秒频率增量 */
ost->tincr2 = 2 * M_PI * 110.0 / c->sample_rate / c->sample_rate;
if (c->codec->capabilities & AV_CODEC_CAP_VARIABLE_FRAME_SIZE)
nb_samples = 10000;
else
nb_samples = c->frame_size;
ost->frame = alloc_audio_frame(c->sample_fmt, c->channel_layout,
c->sample_rate, nb_samples);
ost->tmp_frame = alloc_audio_frame(AV_SAMPLE_FMT_S16, c->channel_layout,
c->sample_rate, nb_samples);
/* 拷贝流参数到合成器 */
ret = avcodec_parameters_from_context(ost->st->codecpar, c);
if (ret < 0) {
fprintf(stderr, "Could not copy the stream parameters\n");
exit(1);
}
/* 创建重采样上下文 */
ost->swr_ctx = swr_alloc();
if (!ost->swr_ctx) {
fprintf(stderr, "Could not allocate resampler context\n");
exit(1);
}
/* 设置选项 */
av_opt_set_int (ost->swr_ctx, "in_channel_count", c->channels, 0);
av_opt_set_int (ost->swr_ctx, "in_sample_rate", c->sample_rate, 0);
av_opt_set_sample_fmt(ost->swr_ctx, "in_sample_fmt", AV_SAMPLE_FMT_S16, 0);
av_opt_set_int (ost->swr_ctx, "out_channel_count", c->channels, 0);
av_opt_set_int (ost->swr_ctx, "out_sample_rate", c->sample_rate, 0);
av_opt_set_sample_fmt(ost->swr_ctx, "out_sample_fmt", c->sample_fmt, 0);
/* 初始化重采样上下文 */
if ((ret = swr_init(ost->swr_ctx)) < 0) {
fprintf(stderr, "Failed to initialize the resampling context\n");
exit(1);
}
}
/* 准备一个16位的音频帧，样本*/
static AVFrame *get_audio_frame(OutputStream *ost)
{
AVFrame *frame = ost->tmp_frame;
int j, i, v;
int16_t *q = (int16_t*)frame->data[0];
/* 检查是否要产生更多的帧 */
AVRational tempratio;
tempratio.num = 1;
tempratio.den = 1;
if (av_compare_ts(ost->next_pts, ost->enc->time_base,
STREAM_DURATION, tempratio) >= 0)
return NULL;
for (j = 0; j <frame->nb_samples; j++) {
v = (int)(sin(ost->t) * 10000);
for (i = 0; i < ost->enc->channels; i++)
*q++ = v;
ost->t += ost->tincr;
ost->tincr += ost->tincr2;
}
frame->pts = ost->next_pts;
ost->next_pts += frame->nb_samples;
return frame;
}
/*
* 编码一个音频帧，发送到合成器
* 编码结束返回1, 其他返回0
*/
static int write_audio_frame(AVFormatContext *oc, OutputStream *ost)
{
AVCodecContext *c;
AVPacket pkt = { 0 }; // 初始化0;
AVFrame *frame;
int ret;
int got_packet;
int dst_nb_samples;
av_init_packet(&pkt);
c = ost->enc;
frame = get_audio_frame(ost);
if (frame) {
/* 样本从初始格式转换为目标格式, 使用重采样器 */
/* 计算目标的样本数*/
dst_nb_samples = av_rescale_rnd(swr_get_delay(ost->swr_ctx, c->sample_rate) + frame->nb_samples,
c->sample_rate, c->sample_rate, AV_ROUND_UP);
av_assert0(dst_nb_samples == frame->nb_samples);
/* 当我们传递一帧给编码器时，可能内部有引用它，此时我们不能写入
*/
ret = av_frame_make_writable(ost->frame);
if (ret < 0)
exit(1);
/* 转换到目标格式 */
ret = swr_convert(ost->swr_ctx,
ost->frame->data, dst_nb_samples,
(const uint8_t **)frame->data, frame->nb_samples);
if (ret < 0) {
fprintf(stderr, "Error while converting\n");
exit(1);
}
frame = ost->frame;
AVRational tempratio;
tempratio.num = 1;
tempratio.den = c->sample_rate;
frame->pts = av_rescale_q(ost->samples_count, tempratio, c->time_base);
ost->samples_count += dst_nb_samples;
}
ret = avcodec_encode_audio2(c, &pkt, frame, &got_packet);
if (ret < 0) {
fprintf(stderr, "Error encoding audio frame: %s\n", av_err2str_f(ret));
exit(1);
}
if (got_packet) {
ret = write_frame(oc, &c->time_base, ost->st, &pkt);
if (ret < 0) {
fprintf(stderr, "Error while writing audio frame: %s\n",
av_err2str_f(ret));
exit(1);
}
}
return (frame || got_packet) ? 0 : 1;
}
/**************************************************************/
/* 视频输出 */
static AVFrame *alloc_picture(enum AVPixelFormat pix_fmt, int width, int height)
{
AVFrame *picture;
int ret;
picture = av_frame_alloc();
if (!picture)
return NULL;
picture->format = pix_fmt;
picture->width = width;
picture->height = height;
/* 分配帧内存 */
ret = av_frame_get_buffer(picture, 32);
if (ret < 0) {
fprintf(stderr, "Could not allocate frame data.\n");
exit(1);
}
return picture;
}
static void open_video(AVFormatContext *oc, AVCodec *codec, OutputStream *ost, AVDictionary *opt_arg)
{
int ret;
AVCodecContext *c = ost->enc;
AVDictionary *opt = NULL;
av_dict_copy(&opt, opt_arg, 0);
/* 打开视频编码器 */
ret = avcodec_open2(c, codec, &opt);
av_dict_free(&opt);
if (ret < 0) {
fprintf(stderr, "Could not open video codec: %s\n", av_err2str_f(ret));
exit(1);
}
/* 分配可复用的帧 */
ost->frame = alloc_picture(c->pix_fmt, c->width, c->height);
if (!ost->frame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(1);
}
/* 如果输出格式不是YUV420P，那么一个也需要一个临时的YUV420P图片，随后可以把它转换为需要的输出格式 */
ost->tmp_frame = NULL;
if (c->pix_fmt != AV_PIX_FMT_YUV420P) {
ost->tmp_frame = alloc_picture(AV_PIX_FMT_YUV420P, c->width, c->height);
if (!ost->tmp_frame) {
fprintf(stderr, "Could not allocate temporary picture\n");
exit(1);
}
}
/* 拷贝流参数到合成器 */
ret = avcodec_parameters_from_context(ost->st->codecpar, c);
if (ret < 0) {
fprintf(stderr, "Could not copy the stream parameters\n");
exit(1);
}
}
/* 准备一帧测试图片. */
static void fill_yuv_image(AVFrame *pict, int frame_index,
int width, int height)
{
int x, y, i;
i = frame_index;
/* Y */
for (y = 0; y < height; y++)
for (x = 0; x < width; x++)
pict->data[0][y * pict->linesize[0] + x] = x + y + i * 3;
/* Cb and Cr */
for (y = 0; y < height / 2; y++) {
for (x = 0; x < width / 2; x++) {
pict->data[1][y * pict->linesize[1] + x] = 128 + y + i * 2;
pict->data[2][y * pict->linesize[2] + x] = 64 + x + i * 5;
}
}
}
static AVFrame *get_video_frame(OutputStream *ost)
{
AVCodecContext *c = ost->enc;
/* 检查是否要生成更多的帧 */
AVRational tempratio;
tempratio.num = 1;
tempratio.den = 1;
if (av_compare_ts(ost->next_pts, c->time_base,
STREAM_DURATION, tempratio) >= 0)
return NULL;
/* 当我们传递一帧给编码器时，可能内部有引用它，此时我们不能写入 */
if (av_frame_make_writable(ost->frame) < 0)
exit(1);
if (c->pix_fmt != AV_PIX_FMT_YUV420P) {
/* 如果必要，从YUV420P转换为目标格式*/
if (!ost->sws_ctx) {
ost->sws_ctx = sws_getContext(c->width, c->height,
AV_PIX_FMT_YUV420P,
c->width, c->height,
c->pix_fmt,
SCALE_FLAGS, NULL, NULL, NULL);
if (!ost->sws_ctx) {
fprintf(stderr,
"Could not initialize the conversion context\n");
exit(1);
}
}
fill_yuv_image(ost->tmp_frame, ost->next_pts, c->width, c->height);
sws_scale(ost->sws_ctx, (const uint8_t * const *) ost->tmp_frame->data,
ost->tmp_frame->linesize, 0, c->height, ost->frame->data,
ost->frame->linesize);
} else {
fill_yuv_image(ost->frame, ost->next_pts, c->width, c->height);
}
ost->frame->pts = ost->next_pts++;
return ost->frame;
}
/*
* 编码视频帧并发送到合成器
* 编码结束返回1, 其他返回0
*/
static int write_video_frame(AVFormatContext *oc, OutputStream *ost)
{
int ret;
AVCodecContext *c;
AVFrame *frame;
int got_packet = 0;
AVPacket pkt = { 0 };
c = ost->enc;
frame = get_video_frame(ost);
av_init_packet(&pkt);
/* 编码图片 */
ret = avcodec_encode_video2(c, &pkt, frame, &got_packet);
if (ret < 0) {
fprintf(stderr, "Error encoding video frame: %s\n", av_err2str_f(ret));
exit(1);
}
if (got_packet) {
ret = write_frame(oc, &c->time_base, ost->st, &pkt);
} else {
ret = 0;
}
if (ret < 0) {
fprintf(stderr, "Error while writing video frame: %s\n", av_err2str_f(ret));
exit(1);
}
return (frame || got_packet) ? 0 : 1;
}
static void close_stream(AVFormatContext *oc, OutputStream *ost)
{
avcodec_free_context(&ost->enc);
av_frame_free(&ost->frame);
av_frame_free(&ost->tmp_frame);
sws_freeContext(ost->sws_ctx);
swr_free(&ost->swr_ctx);
}
int _tmain(int argc, _TCHAR* argvec[])
{
OutputStream video_st = { 0 }, audio_st = { 0 };
const char *filename;
AVOutputFormat *fmt;
AVFormatContext *oc;
AVCodec *audio_codec, *video_codec;
int ret;
int have_video = 0, have_audio = 0;
int encode_video = 0, encode_audio = 0;
AVDictionary *opt = NULL;
av_register_all();
filename = "generated.mp4";
/* 根据文件名的后缀，分配输出格式的上下文 */
avformat_alloc_output_context2(&oc, NULL, NULL, filename);
if (!oc) {
printf("Could not deduce output format from file extension: using MPEG.\n");
avformat_alloc_output_context2(&oc, NULL, "mpeg", filename);
}
if (!oc)
return 1;
//得到输出格式
fmt = oc->oformat;
/* 使用默认格式的编码器，增加音频和视频流
* 初始化编码器 */
if (fmt->video_codec != AV_CODEC_ID_NONE) {
add_stream(&video_st, oc, &video_codec, fmt->video_codec);
have_video = 1;
encode_video = 1;
}
if (fmt->audio_codec != AV_CODEC_ID_NONE) {
add_stream(&audio_st, oc, &audio_codec, fmt->audio_codec);
have_audio = 1;
encode_audio = 1;
}
/* 设置所有的参数，打开音频和视频编码器，分配必要的编码内存*/
if (have_video)
open_video(oc, video_codec, &video_st, opt);
if (have_audio)
open_audio(oc, audio_codec, &audio_st, opt);
//打印输出流的信息
av_dump_format(oc, 0, filename, 1);
/* 打开输出文件 */
if (!(fmt->flags & AVFMT_NOFILE)) {
ret = avio_open(&oc->pb, filename, AVIO_FLAG_WRITE);
if (ret < 0) {
fprintf(stderr, "Could not open '%s': %s\n", filename,
av_err2str_f(ret));
return 1;
}
}
/* 写入流的头部 */
ret = avformat_write_header(oc, &opt);
if (ret < 0) {
fprintf(stderr, "Error occurred when opening output file: %s\n",
av_err2str_f(ret));
return 1;
}
while (encode_video || encode_audio) {
/* 选择流进行编码 */
if (encode_video &&
(!encode_audio || av_compare_ts(video_st.next_pts, video_st.enc->time_base,
audio_st.next_pts, audio_st.enc->time_base) <= 0)) {
encode_video = !write_video_frame(oc, &video_st);
} else {
encode_audio = !write_audio_frame(oc, &audio_st);
}
}
/* 写入流的尾部 */
av_write_trailer(oc);
/* 关闭编码器. */
if (have_video)
close_stream(oc, &video_st);
if (have_audio)
close_stream(oc, &audio_st);
if (!(fmt->flags & AVFMT_NOFILE))
/* 关闭输出文件*/
avio_closep(&oc->pb);
/* 释放编码上下文 */
avformat_free_context(oc);
system("PAUSE");
return 0;
}