• 音视频从入门到精通——FFmpeg之av_seek_frame函数分析

    文章目录

    播放器进度条函数av_seek_frame分析

    av_seek_frame函数分析
    在这里插入图片描述

    /**
 * Seek to the keyframe at timestamp.
 * 'timestamp' in 'stream_index'.
 *
 * @param s media file handle
 * @param stream_index If stream_index is (-1), a default
 * stream is selected, and timestamp is automatically converted
 * from AV_TIME_BASE units to the stream specific time_base.
 * @param timestamp Timestamp in AVStream.time_base units
 *        or, if no stream is specified, in AV_TIME_BASE units.
 * @param flags flags which select direction and seeking mode
 * @return >= 0 on success
 */
int av_seek_frame(AVFormatContext *s, int stream_index, int64_t timestamp,
                  int flags);

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    参数说明：

    s: AVFormatContext类型的多媒体文件句柄

    stream_index : int类型表示要进行操作的流索引

    timestamp: int64_t类型的时间戳，表示要跳转到的时间位置

    flags : 跳转方法，主要有一下几种

    #define AVSEEK_FLAG_BACKWARD 1 
///< seek backward seek到timestamp之前的最近关键帧

#define AVSEEK_FLAG_BYTE 2 
///< seeking based on position in bytes 基于字节位置的跳转

#define AVSEEK_FLAG_ANY 4 
///< seek to any frame, even non-keyframes 跳转到任意帧，不一定是关键帧

#define AVSEEK_FLAG_FRAME 8 
///< seeking based on frame number 基于帧数量的跳转

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    flags 的值为1，2，4，8。表示为二进制也就是

    0000 0001
0000 0010
0000 1000
1000 0000

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    所以，flags 应该是要通过或运算，加起来使用的。
    使用方法
    在这里插入图片描述

    代码

    

#include 
#include 
extern "C" {
	#include "libavformat/avformat.h"
	#include "libavcodec/avcodec.h"
	#include "libswscale/swscale.h"
	#include "libswresample/swresample.h"
}
using namespace std;

#pragma comment(lib,"avformat.lib")
#pragma comment(lib,"avutil.lib")
#pragma comment(lib,"avcodec.lib")
#pragma comment(lib,"swscale.lib")
#pragma comment(lib,"swresample.lib")

static double r2d(AVRational r)
{
	return r.den == 0 ? 0 : (double)r.num / (double)r.den;
}

void XSleep(int ms)
{
	//c++ 11
	chrono::milliseconds du(ms);
	this_thread::sleep_for(du);
}

int main(int argc, char* argv[])
{

	cout << "Test Demux FFmpeg.club" << endl;
	const char* path = "D:\\javaCode\\androidmaniu2022\\FFmpeg\\input.mp4";
	//初始化封装库---declared deprecated
	//---av_register_all();

	//初始化网络库 （可以打开rtsp rtmp http 协议的流媒体视频）
	avformat_network_init();

	//注册解码器---declared deprecated
	//avcodec_register_all();

	//参数设置
	AVDictionary* opts = NULL;
	//设置rtsp流已tcp协议打开
	av_dict_set(&opts, "rtsp_transport", "tcp", 0);

	//网络延时时间
	av_dict_set(&opts, "max_delay", "500", 0);


	//解封装上下文
	AVFormatContext* ic = NULL;
	int re = avformat_open_input(
		&ic,
		path,
		0,  // 0表示自动选择解封器
		&opts //参数设置，比如rtsp的延时时间
	);
	if (re != 0)
	{
		char buf[1024] = { 0 };
		av_strerror(re, buf, sizeof(buf) - 1);
		cout << "open " << path << " failed! :" << buf << endl;
		getchar();
		return -1;
	}
	cout << "open " << path << " success! " << endl;

	//获取流信息 
	re = avformat_find_stream_info(ic, 0);

	//总时长 毫秒
	int totalMs = ic->duration / (AV_TIME_BASE / 1000);
	cout << "totalMs = " << totalMs << endl;

	//打印视频流详细信息
	av_dump_format(ic, 0, path, 0);

	//音视频索引，读取时区分音视频
	int videoStream = 0;
	int audioStream = 1;

	//获取音视频流信息 （遍历，函数获取）
	for (int i = 0; i < ic->nb_streams; i++)
	{
		AVStream* as = ic->streams[i];
		cout << "codec_id = " << as->codecpar->codec_id << endl;
		cout << "format = " << as->codecpar->format << endl;

		//音频 AVMEDIA_TYPE_AUDIO
		if (as->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)
		{
			audioStream = i;
			cout << i << "音频信息" << endl;
			cout << "sample_rate = " << as->codecpar->sample_rate << endl;
			//AVSampleFormat;
			cout << "channels = " << as->codecpar->channels << endl;
			//一帧数据？？ 单通道样本数 
			cout << "frame_size = " << as->codecpar->frame_size << endl;
			//1024 * 2 * 2 = 4096  fps = sample_rate/frame_size

		}
		//视频 AVMEDIA_TYPE_VIDEO
		else if (as->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
		{
			videoStream = i;
			cout << i << "视频信息" << endl;
			cout << "width=" << as->codecpar->width << endl;
			cout << "height=" << as->codecpar->height << endl;
			//帧率 fps 分数转换
			cout << "video fps = " << r2d(as->avg_frame_rate) << endl;
		}
	}

	//获取视频流
	videoStream = av_find_best_stream(ic, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);

	//
	///视频解码器打开
	///找到视频解码器
	AVCodec* vcodec = avcodec_find_decoder(ic->streams[videoStream]->codecpar->codec_id);
	if (!vcodec)
	{
		cout << "can't find the codec id " << ic->streams[videoStream]->codecpar->codec_id;
		getchar();
		return -1;
	}
	cout << "find the AVCodec " << ic->streams[videoStream]->codecpar->codec_id << endl;

	AVCodecContext* vc = avcodec_alloc_context3(vcodec);

	///配置解码器上下文参数
	avcodec_parameters_to_context(vc, ic->streams[videoStream]->codecpar);
	//八线程解码
	vc->thread_count = 8;

	///打开解码器上下文
	re = avcodec_open2(vc, 0, 0);
	if (re != 0)
	{
		char buf[1024] = { 0 };
		av_strerror(re, buf, sizeof(buf) - 1);
		cout << "avcodec_open2  failed! :" << buf << endl;
		getchar();
		return -1;
	}
	cout << "video avcodec_open2 success!" << endl;


	//
	///音频解码器打开
	AVCodec* acodec = avcodec_find_decoder(ic->streams[audioStream]->codecpar->codec_id);
	if (!acodec)
	{
		cout << "can't find the codec id " << ic->streams[audioStream]->codecpar->codec_id;
		getchar();
		return -1;
	}
	cout << "find the AVCodec " << ic->streams[audioStream]->codecpar->codec_id << endl;
	///创建解码器上下文呢
	AVCodecContext* ac = avcodec_alloc_context3(acodec);

	///配置解码器上下文参数
	avcodec_parameters_to_context(ac, ic->streams[audioStream]->codecpar);
	//八线程解码
	ac->thread_count = 8;

	///打开解码器上下文
	re = avcodec_open2(ac, 0, 0);
	if (re != 0)
	{
		char buf[1024] = { 0 };
		av_strerror(re, buf, sizeof(buf) - 1);
		cout << "avcodec_open2  failed! :" << buf << endl;
		getchar();
		return -1;
	}
	cout << "audio avcodec_open2 success!" << endl;

	///ic->streams[videoStream]
	//malloc AVPacket并初始化
	AVPacket* pkt = av_packet_alloc();
	AVFrame* frame = av_frame_alloc();

	//像素格式和尺寸转换上下文
	SwsContext* vctx = NULL;
	unsigned char* rgb = NULL;

	//音频重采样 上下文初始化
	SwrContext* actx = swr_alloc();
	actx = swr_alloc_set_opts(actx,
		av_get_default_channel_layout(2),	//输出格式
		AV_SAMPLE_FMT_S16,					//输出样本格式
		ac->sample_rate,					//输出采样率
		av_get_default_channel_layout(ac->channels),//输入格式
		ac->sample_fmt,
		ac->sample_rate,
		0, 0
	);
	re = swr_init(actx);
	if (re != 0)
	{
		char buf[1024] = { 0 };
		av_strerror(re, buf, sizeof(buf) - 1);
		cout << "swr_init  failed! :" << buf << endl;
		getchar();
		return -1;
	}
	unsigned char* pcm = NULL;

	for (;;)
	{
		int re = av_read_frame(ic, pkt);
		if (re != 0)
		{
			//循环播放
			cout << "==============================end==============================" << endl;
			int ms = 3000; //三秒位置 根据时间基数（分数）转换
			long long pos = (double)ms / (double)1000 * r2d(ic->streams[pkt->stream_index]->time_base);
			av_seek_frame(ic, videoStream, pos, AVSEEK_FLAG_BACKWARD | AVSEEK_FLAG_FRAME);
			continue;
		}
		cout << "pkt->size = " << pkt->size << endl;

		//显示的时间
		cout << "pkt->pts = " << pkt->pts << "(单位：秒)" << endl;
		//转换为毫秒，方便做同步
		cout << "pkt->pts ms = " << pkt->pts * (r2d(ic->streams[pkt->stream_index]->time_base) * 1000) << "(单位：毫秒)" << endl;



		//解码时间
		cout << "pkt->dts = " << pkt->dts << endl;

		AVCodecContext* cc = 0;
		if (pkt->stream_index == videoStream)
		{
			cout << "图像" << endl;
			cc = vc;


		}
		if (pkt->stream_index == audioStream)
		{
			cout << "音频" << endl;
			cc = ac;
		}

		///解码视频
		//发送packet到解码线程  send传NULL后调用多次receive取出所有缓冲帧
		re = avcodec_send_packet(cc, pkt);
		//释放，引用计数-1 为0释放空间
		av_packet_unref(pkt);

		if (re != 0)
		{
			char buf[1024] = { 0 };
			av_strerror(re, buf, sizeof(buf) - 1);
			cout << "avcodec_send_packet  failed! :" << buf << endl;
			continue;
		}

		
		for (;;)
		{
			//从线程中获取解码接口,一次send可能对应多次receive
			re = avcodec_receive_frame(cc, frame);
			//直到收不到为止,break退出循环
			if (re != 0) break;


			if (cc == vc) {//视频
				cout << "recv frame format      = " << frame->format << endl;
				cout << "recv frame linesize[0] = " << frame->linesize[0] << endl;
				cout << "recv frame linesize[1] = " << frame->linesize[1] << endl;
				cout << "recv frame linesize[2] = " << frame->linesize[2] << endl;
				//cout << endl;
			}else {//音频
				cout << "recv frame format      = " << frame->format << endl;
				cout << "recv frame linesize[0] = " << frame->linesize[0] << endl;
				cout << "recv frame nb_samples  = " << frame->nb_samples << endl;
			}


			//视频
			if (cc == vc)
			{

				vctx = sws_getCachedContext(
					vctx,	//传NULL会新创建
					frame->width, frame->height,	//输入的宽高
					(AVPixelFormat)frame->format,	//输入格式 YUV420p
					frame->width, frame->height,	//输出的宽高
					AV_PIX_FMT_RGBA,				//输出格式RGBA
					SWS_BILINEAR,					//尺寸变化的算法
					0, 0, 0);
				//if(vctx)
					//cout << "像素格式尺寸转换上下文创建或者获取成功！" << endl;
				//else
				//	cout << "像素格式尺寸转换上下文创建或者获取失败！" << endl;
				if (vctx)
				{
					if (!rgb) rgb = new unsigned char[frame->width * frame->height * 4];
					uint8_t* data[2] = { 0 };
					data[0] = rgb;
					int lines[2] = { 0 };
					lines[0] = frame->width * 4;
					re = sws_scale(vctx,
						frame->data,		//输入数据
						frame->linesize,	//输入行大小
						0,
						frame->height,		//输入高度
						data,				//输出数据和大小
						lines
					);
					cout << "sws_scale = " << re << endl;
				}

			}
			else //音频
			{
				uint8_t* data[2] = { 0 };
				if (!pcm) pcm = new uint8_t[frame->nb_samples * 2 * 2];
				data[0] = pcm;
				re = swr_convert(actx,
					data, frame->nb_samples,		//输出
					(const uint8_t**)frame->data, frame->nb_samples	//输入
				);
				cout << "swr_convert = " << re << endl;
			}

		}



		//XSleep(500);
	}
	av_frame_free(&frame);
	av_packet_free(&pkt);



	if (ic)
	{
		//释放封装上下文，并且把ic置0
		avformat_close_input(&ic);
	}

	getchar();
	return 0;
}

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    参考
    ffmpeg中av_seek_frame使用样例
    FFMPEG av_seek_frame

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  • 原文地址：https://blog.csdn.net/e891377/article/details/126705854