FFmpeg 源码分析：av_seek

@[TOC](FFmpeg 源码分析：av_seek_frame())

FFmpeg 源码分析：av_seek_frame()

函数原型

av_seek_frame() 是 FFmpeg 中的一个函数，位于 libavformat/avformat.h，用于定位媒体文件中的某一帧。

下面是 av_seek_frame() 的函数定义：

/*** 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);

参数说明：

AVFormatContext *s：流媒体打开的上下文结构指针。
stream_index：需要定位的音视频流的索引。一般0为视频流索引，1为音频流索引；-1为默认，说明是所有的媒体流同时跳转。
timestamp：定位的时间戳。在 FFmpeg 中，时间戳（timestamp）的单位是时间基数（time_base），时间戳值乘以时间基，可以得到实际的时刻值（以秒等为单位）。
flags：设置跳转模式。该参数一共有以下四种具体取值：
```
#define AVSEEK_FLAG_BACKWARD 1 ///< seek backward
#define AVSEEK_FLAG_BYTE     2 ///< seeking based on position in bytes
#define AVSEEK_FLAG_ANY      4 ///< seek to any frame, even non-keyframes
#define AVSEEK_FLAG_FRAME    8 ///< seeking based on frame number
```
下面来详细解释一下：
- AVSEEK_FLAG_BACKWARD：定位到请求的时间戳之前最近的关键帧
- AVSEEK_FLAG_BYTE：基于字节位置的跳转，当采用这个 flags 时，时间戳要改为 byte 字节计数。
- AVSEEK_FLAG_ANY：任意定位，跳转到任意帧，不一定是关键帧，因此使用时可能会导致花屏。
- AVSEEK_FLAG_FRAME：强制定位到最接近的关键帧。
此外，flags 可以通过或运算组合起来使用。

返回值：返回值大于等于 0，代表打开成功，否则失败。

需要注意的是，使用 av_seek_frame() 函数进行定位时，必须保证输入格式上下文中的流信息已经完全读取，否则可能会出现定位失败的情况。

使用细节

seek操作基准：即seek操作当前时间点，因此在进行播放时需要实时记录音视频流的DTS或者PTS。
seek时间单位：进行seek操作时，根据流索引，确定其时间单位time_base。
seek时间大小：即向前或者向后seek的时间大小，根据此时间大小和当前时间点，可以计算出向前或者向后进行seek操作时的目标时间。
seek操作载体：即是按照音频还是视频进行seek操作，只需要按照其中一个流进行seek即可，不需要分别对音视频流进行seek操作。
seek操作刷新：在进行seek操作之后，正常播放之前需要将编解码的内部缓冲区进行刷新，同时也要将自行控制的缓冲区内缓存的音视频清零。

实例：循环播放、可快进快退的播放器

参考：https://blog.csdn.net/zhaoyun_zzz/article/details/89406087

unistd.h 导入：https://www.cnblogs.com/lutaishi/p/13436265.html
新建一个 unistd.h，内容如下：

/** This file is part of the Mingw32 package.*  unistd.h maps     (roughly) to io.h*/
#ifndef _UNISTD_H
#define _UNISTD_H
#include <io.h>
#include <process.h>
#endif /* _UNISTD_H */

放到 Visual Studio VC 文件夹的 include 下，我的路径是：C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include。

pthread.h 导入：https://blog.csdn.net/Hexa_H/article/details/130691024

// Simplest FFmpeg Seek Player.cpp : 定义控制台应用程序的入口点。
//#include "stdafx.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <windows.h>
#define __STDC_CONSTANT_MACROS#ifdef __cplusplus
extern "C"
{
#endif
#include <libavutil/time.h>
#include <libavutil/imgutils.h>
#include <libavutil/mathematics.h>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavdevice/avdevice.h>
#include <libswscale/swscale.h>
#include <libswresample/swresample.h>
#include <SDL2/SDL.h>#include <errno.h>#include <unistd.h>
#include <assert.h>
#include <pthread.h>
#include <semaphore.h>#ifdef __cplusplus
};
#endif// 报错：
// LNK2019 无法解析的外部符号 __imp__fprintf，该符号在函数 _ShowError 中被引用
// LNK2019 无法解析的外部符号 __imp____iob_func，该符号在函数 _ShowError 中被引用// 解决办法：
// 包含库的编译器版本低于当前编译版本，需要将包含库源码用vs2017重新编译，由于没有包含库的源码，此路不通。
// 然后查到说是stdin, stderr, stdout 这几个函数vs2015和以前的定义得不一样，所以报错。
// 解决方法呢，就是使用{ *stdin,*stdout,*stderr }数组自己定义__iob_func()
#pragma comment(lib,"legacy_stdio_definitions.lib")
extern "C"
{FILE __iob_func[3] = { *stdin, *stdout, *stderr };
}#define MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio#define PACKET_ARRAY_SIZE			(60)
typedef struct __PacketStruct
{AVPacket Packet;int64_t dts;int64_t pts;int state;
}PacketStruct;typedef struct
{unsigned int rIndex;unsigned int wIndex;PacketStruct PacketArray[PACKET_ARRAY_SIZE];
}PacketArrayStruct;typedef struct __AudioCtrlStruct
{AVFormatContext	*pFormatCtx;AVStream 		*pStream;AVCodec			*pCodec;AVCodecContext	*pCodecCtx;SwrContext 		*pConvertCtx;Uint8  	*audio_chunk;Sint32  audio_len;Uint8  	*audio_pos;int 	AudioIndex;int 	AudioCnt;uint64_t AudioOutChannelLayout;int out_nb_samples;				// nb_samples: AAC-1024 MP3-1152AVSampleFormat out_sample_fmt;int out_sample_rate;int out_channels;int out_buffer_size;unsigned char* pAudioOutBuffer;sem_t frame_put;sem_t frame_get;PacketArrayStruct 	Audio;
}AudioCtrlStruct;typedef struct __VideoCtrlStruct
{AVFormatContext	*pFormatCtx;AVStream 		*pStream;AVCodec			*pCodec;AVCodecContext	*pCodecCtx;SwsContext 		*pConvertCtx;AVFrame			*pVideoFrame, *pFrameYUV;unsigned char 	*pVideoOutBuffer;int 			VideoIndex;int 			VideoCnt;int 			RefreshTime;int screen_w, screen_h;SDL_Window *screen;SDL_Renderer* sdlRenderer;SDL_Texture* sdlTexture;SDL_Rect sdlRect;SDL_Thread *video_tid;sem_t frame_put;sem_t video_refresh;PacketArrayStruct Video;
}VideoCtrlStruct;//Refresh Event
#define SFM_REFRESH_VIDEO_EVENT  	(SDL_USEREVENT + 1)
#define SFM_REFRESH_AUDIO_EVENT  	(SDL_USEREVENT + 2)
#define SFM_BREAK_EVENT  			(SDL_USEREVENT + 3)int thread_exit = 0;
int thread_pause = 0;
int audio_pause = 0;		//音频播放是否暂停，1表示暂停，0表示在播放
int video_pause = 0;		//视频播放是否暂停，1表示暂停，0表示在播放
SDL_Keycode CurKeyCode;		//记录按下的是前进还是后退键，即小键盘的左右方向键，右表示前进，左表示后退
int CurKeyProcess;			//按键seek操作是否已经被处理，0表示未处理，1表示已经处理
int64_t CurVideoDts;	//记录当前播放的视频流Packet的DTS
int64_t CurVideoPts;	//记录当前播放的视频流Packet的DTSint64_t CurAudioDts;	//记录当前播放的音频流Packet的DTS
int64_t CurAudioPts;	//记录当前播放的音频流Packet的DTSint64_t DstAudioDts;	//进行seek操作时，计算后的目标音频流的DTS
int64_t DstAudioPts;	//进行seek操作时，计算后的目标音频流的PTS
int64_t DstVideoDts;	//进行seek操作时，计算后的目标视频流的DTS
int64_t DstVideoPts;	//进行seek操作时，计算后的目标视频流的DTSVideoCtrlStruct VideoCtrl;
AudioCtrlStruct AudioCtrl;
//video time_base.num:1, time_base.den:16, avg_frame_rate.num:8, avg_frame_rate.den:1
//audio time_base.num:1, time_base.den:48000, avg_frame_rate.num:0, avg_frame_rate.den:0
int IsPacketArrayFull(PacketArrayStruct* p)
{int i = 0;i = p->wIndex % PACKET_ARRAY_SIZE;if (p->PacketArray[i].state != 0) return 1;return 0;
}int IsPacketArrayEmpty(PacketArrayStruct* p)
{int i = 0;i = p->rIndex % PACKET_ARRAY_SIZE;if (p->PacketArray[i].state == 0) return 1;return 0;
}int PacketArrayClear(PacketArrayStruct* p)
{int i = 0;for (i = 0; i < PACKET_ARRAY_SIZE; i++){if (p->PacketArray[i].state != 0){av_packet_unref(&p->PacketArray[i].Packet);p->PacketArray[i].state = 0;}}p->rIndex = 0;p->wIndex = 0;return 0;
}int SDL_event_thread(void *opaque)
{SDL_Event event;while (1){SDL_WaitEvent(&event);if (event.type == SDL_KEYDOWN){//Pauseif (event.key.keysym.sym == SDLK_SPACE){thread_pause = !thread_pause;printf("video got pause event!\n");}if (event.key.keysym.sym == SDLK_RIGHT){thread_pause = !thread_pause;CurKeyProcess = 0;CurKeyCode = SDLK_RIGHT;printf("video got right key event!\n");}if (event.key.keysym.sym == SDLK_LEFT){thread_pause = !thread_pause;CurKeyProcess = 0;CurKeyCode = SDLK_LEFT;printf("video got left key event!\n");}}else if (event.type == SDL_QUIT){thread_exit = 1;printf("------------------------------>video got SDL_QUIT event!\n");break;}else if (event.type == SFM_BREAK_EVENT){break;}}printf("---------> SDL_event_thread end !!!! \n");return 0;
}int video_refresh_thread(void *opaque)
{while (1){if (thread_exit) break;if (thread_pause){SDL_Delay(40);continue;}//SDL_Delay(40);Sleep(VideoCtrl.RefreshTime);sem_post(&VideoCtrl.video_refresh);}printf("---------> video_refresh_thread end !!!! \n");return 0;
}static void *thread_audio(void *arg)
{AVCodecContext	*pAudioCodecCtx;AVFrame			*pAudioFrame;unsigned char 	*pAudioOutBuffer;AVPacket 		*Packet;int 			i, ret, GotAudioPicture;struct SwrContext *AudioConvertCtx;AudioCtrlStruct* AudioCtrl = (AudioCtrlStruct*)arg;pAudioCodecCtx = AudioCtrl->pCodecCtx;pAudioOutBuffer = AudioCtrl->pAudioOutBuffer;AudioConvertCtx = AudioCtrl->pConvertCtx;printf("---------> thread_audio start !!!! \n");pAudioFrame = av_frame_alloc();while (1){if (thread_exit) break;if (thread_pause){Sleep(10000);audio_pause = 1;continue;}if (IsPacketArrayEmpty(&AudioCtrl->Audio)){SDL_Delay(1);printf("---------> thread_audio empty !!!! \n");continue;}audio_pause = 0;i = AudioCtrl->Audio.rIndex;Packet = &AudioCtrl->Audio.PacketArray[i].Packet;CurAudioDts = AudioCtrl->Audio.PacketArray[i].dts;CurAudioPts = AudioCtrl->Audio.PacketArray[i].pts;if (Packet->stream_index == AudioCtrl->AudioIndex){// ret = avcodec_decode_audio4(pAudioCodecCtx, pAudioFrame, &GotAudioPicture, Packet);ret = avcodec_send_packet(pAudioCodecCtx, Packet);if (ret < 0){printf("Error in decoding audio frame.\n");return 0;}while (avcodec_receive_frame(pAudioCodecCtx, pAudioFrame) == 0){swr_convert(AudioConvertCtx, &pAudioOutBuffer, MAX_AUDIO_FRAME_SIZE,(const uint8_t **)pAudioFrame->data, pAudioFrame->nb_samples);printf("Auduo index:%5d\t pts:%ld\t packet size:%d, pFrame->nb_samples:%d\n",AudioCtrl->AudioCnt, Packet->pts, Packet->size, pAudioFrame->nb_samples);AudioCtrl->AudioCnt++;}while (AudioCtrl->audio_len > 0)//Wait until finishSDL_Delay(1);//Set audio buffer (PCM data)AudioCtrl->audio_chunk = (Uint8 *)pAudioOutBuffer;AudioCtrl->audio_pos = AudioCtrl->audio_chunk;AudioCtrl->audio_len = AudioCtrl->out_buffer_size;av_packet_unref(Packet);AudioCtrl->Audio.PacketArray[i].state = 0;i++;if (i >= PACKET_ARRAY_SIZE) i = 0;AudioCtrl->Audio.rIndex = i;}}printf("---------> thread_audio end !!!! \n");return 0;
}static void *thread_video(void *arg)
{//AVFormatContext	*pFormatCtx;AVCodecContext	*pVideoCodecCtx;//AVCodec			*pVideoCodec;AVFrame			*pVideoFrame, *pFrameYUV;//unsigned char 	*pVideoOutBuffer;AVPacket 		*Packet;int 			i, ret, GotPicture;struct SwsContext *VideoConvertCtx;VideoCtrlStruct* VideoCtrl = (VideoCtrlStruct*)arg;pVideoCodecCtx = VideoCtrl->pCodecCtx;//pVideoOutBuffer = VideoCtrl->pVideoOutBuffer;VideoConvertCtx = VideoCtrl->pConvertCtx;pVideoFrame = VideoCtrl->pVideoFrame;pFrameYUV = VideoCtrl->pFrameYUV;printf("---------> thread_video start !!!! \n");while (1){if (thread_exit) break;if (thread_pause){Sleep(10000);video_pause = 1;continue;}if (IsPacketArrayEmpty(&VideoCtrl->Video)){SDL_Delay(1);continue;}video_pause = 0;i = VideoCtrl->Video.rIndex;Packet = &VideoCtrl->Video.PacketArray[i].Packet;CurVideoDts = VideoCtrl->Video.PacketArray[i].dts;CurVideoPts = VideoCtrl->Video.PacketArray[i].pts;if (Packet->stream_index == VideoCtrl->VideoIndex){// ret = avcodec_decode_video2(pVideoCodecCtx, pVideoFrame, &GotPicture, Packet);ret = avcodec_send_packet(pVideoCodecCtx, Packet);if (ret != 0){printf("Video Decode Error.\n");return 0;}GotPicture = avcodec_receive_frame(pVideoCodecCtx, pVideoFrame);printf("Video index:%5d\t dts:%ld\t, pts:%ld\t packet size:%d, GotVideoPicture:%d\n",VideoCtrl->VideoCnt, Packet->dts, Packet->pts, Packet->size, GotPicture);//			printf("Video index:%5d\t pFrame->pkt_dts:%ld, pFrame->pkt_pts:%ld, pFrame->pts:%ld, pFrame->pict_type:%d, "//					"pFrame->best_effort_timestamp:%ld, pFrame->pkt_pos:%ld, pVideoFrame->pkt_duration:%ld\n",//					VideoCtrl->VideoCnt, pVideoFrame->pkt_dts, pVideoFrame->pkt_pts, pVideoFrame->pts,//					pVideoFrame->pict_type, pVideoFrame->best_effort_timestamp,//					pVideoFrame->pkt_pos, pVideoFrame->pkt_duration);VideoCtrl->VideoCnt++;if (GotPicture == 0){sws_scale(VideoConvertCtx, (const unsigned char* const*)pVideoFrame->data,pVideoFrame->linesize, 0, pVideoCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);sem_wait(&VideoCtrl->video_refresh);//SDL---------------------------SDL_UpdateTexture(VideoCtrl->sdlTexture, NULL, pFrameYUV->data[0], pFrameYUV->linesize[0]);SDL_RenderClear(VideoCtrl->sdlRenderer);//SDL_RenderCopy( sdlRenderer, sdlTexture, &sdlRect, &sdlRect );SDL_RenderCopy(VideoCtrl->sdlRenderer, VideoCtrl->sdlTexture, NULL, NULL);SDL_RenderPresent(VideoCtrl->sdlRenderer);//SDL End-----------------------}av_packet_unref(Packet);VideoCtrl->Video.PacketArray[i].state = 0;i++;if (i >= PACKET_ARRAY_SIZE) i = 0;VideoCtrl->Video.rIndex = i;}}printf("---------> thread_video end !!!! \n");return 0;
}/* The audio function callback takes the following parameters:
* stream: A pointer to the audio buffer to be filled
* len: The length (in bytes) of the audio buffer
*/
void fill_audio(void *udata, Uint8 *stream, int len)
{AudioCtrlStruct* AudioCtrl = (AudioCtrlStruct*)udata;//SDL 2.0SDL_memset(stream, 0, len);if (AudioCtrl->audio_len == 0) return;len = (len > AudioCtrl->audio_len ? AudioCtrl->audio_len : len);	/*  Mix  as  much  data  as  possible  */SDL_MixAudio(stream, AudioCtrl->audio_pos, len, SDL_MIX_MAXVOLUME);AudioCtrl->audio_pos += len;AudioCtrl->audio_len -= len;
}AVFormatContext	*pFormatCtx;
AVCodecContext	*pVideoCodecCtx, *pAudioCodecCtx;
AVCodec			*pVideoCodec, *pAudioCodec;
AVCodecParameters *pVideoCodecParameters, *pAudioCodecParameters;
AVPacket		*Packet;
unsigned char 	*pVideoOutBuffer, *pAudioOutBuffer;int 			ret;
unsigned int    i;
pthread_t 		audio_tid, video_tid;uint64_t AudioOutChannelLayout;
//nb_samples: AAC-1024 MP3-1152
int out_nb_samples;
AVSampleFormat out_sample_fmt;
int out_sample_rate;
int out_channels;
//Out Buffer Size
int out_buffer_size;//------------SDL----------------struct SwsContext *VideoConvertCtx;
struct SwrContext *AudioConvertCtx;
int VideoIndex, VideoCnt;
int AudioIndex, AudioCnt;int main(int argc, char* argv[])
{char *filepath = "cuc_ieschool.mp4";memset(&AudioCtrl, 0, sizeof(AudioCtrlStruct));memset(&VideoCtrl, 0, sizeof(VideoCtrlStruct));sem_init(&VideoCtrl.video_refresh, 0, 0);sem_init(&VideoCtrl.frame_put, 0, 0);sem_init(&AudioCtrl.frame_put, 0, 0);thread_exit = 0;thread_pause = 0;CurKeyProcess = 1;CurKeyCode = 0;// av_register_all();avformat_network_init();pFormatCtx = avformat_alloc_context();if (avformat_open_input(&pFormatCtx, filepath, NULL, NULL) != 0){printf("Couldn't open input stream.\n");return -1;}if (avformat_find_stream_info(pFormatCtx, NULL) < 0){printf("Couldn't find stream information.\n");return -1;}VideoIndex = -1;AudioIndex = -1;for (i = 0; i < pFormatCtx->nb_streams; i++){if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO){VideoIndex = i;//打印输出视频流的信息printf("video time_base.num:%d, time_base.den:%d, avg_frame_rate.num:%d, avg_frame_rate.den:%d\n",pFormatCtx->streams[VideoIndex]->time_base.num,pFormatCtx->streams[VideoIndex]->time_base.den,pFormatCtx->streams[VideoIndex]->avg_frame_rate.num,pFormatCtx->streams[VideoIndex]->avg_frame_rate.den);}if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO){AudioIndex = i;//打印输出音频流的信息//pFormatCtx->streams[AudioIndex]->time_base.den <<= 1;printf("audio time_base.num:%d, time_base.den:%d, avg_frame_rate.num:%d, avg_frame_rate.den:%d\n",pFormatCtx->streams[AudioIndex]->time_base.num,pFormatCtx->streams[AudioIndex]->time_base.den,pFormatCtx->streams[AudioIndex]->avg_frame_rate.num,pFormatCtx->streams[AudioIndex]->avg_frame_rate.den);}}if (VideoIndex != -1){	// 准备视频的解码操作上下文数据结构pVideoCodec = avcodec_find_decoder(pFormatCtx->streams[VideoIndex]->codecpar->codec_id);pVideoCodecCtx = avcodec_alloc_context3(pVideoCodec);pVideoCodecParameters = pFormatCtx->streams[VideoIndex]->codecpar;avcodec_parameters_to_context(pVideoCodecCtx, pVideoCodecParameters);if (pVideoCodec == NULL){printf("Video Codec not found.\n");return -1;}if (avcodec_open2(pVideoCodecCtx, pVideoCodec, NULL) < 0){printf("Could not open video codec.\n");return -1;}// prepare videoVideoCtrl.pVideoFrame = av_frame_alloc();VideoCtrl.pFrameYUV = av_frame_alloc();ret = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pVideoCodecCtx->width, pVideoCodecCtx->height, 1);pVideoOutBuffer = (unsigned char *)av_malloc(ret);av_image_fill_arrays(VideoCtrl.pFrameYUV->data, VideoCtrl.pFrameYUV->linesize, pVideoOutBuffer,AV_PIX_FMT_YUV420P, pVideoCodecCtx->width, pVideoCodecCtx->height, 1);VideoConvertCtx = sws_getContext(pVideoCodecCtx->width, pVideoCodecCtx->height, pVideoCodecCtx->pix_fmt,pVideoCodecCtx->width, pVideoCodecCtx->height,AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);VideoCtrl.pFormatCtx = pFormatCtx;VideoCtrl.pStream = pFormatCtx->streams[VideoIndex];VideoCtrl.pCodec = pVideoCodec;// VideoCtrl.pCodecCtx = pFormatCtx->streams[VideoIndex]->codec;pVideoCodecParameters = pFormatCtx->streams[VideoIndex]->codecpar;AVCodecContext *pVideoCodecContext = avcodec_alloc_context3(NULL);avcodec_parameters_to_context(pVideoCodecContext, pVideoCodecParameters);VideoCtrl.pCodecCtx = pVideoCodecContext;VideoCtrl.pConvertCtx = VideoConvertCtx;VideoCtrl.pVideoOutBuffer = pVideoOutBuffer;VideoCtrl.VideoIndex = VideoIndex;if (pFormatCtx->streams[VideoIndex]->avg_frame_rate.num == 0 ||pFormatCtx->streams[VideoIndex]->avg_frame_rate.den == 0){VideoCtrl.RefreshTime = 40000;}else{VideoCtrl.RefreshTime = 1000000 * pFormatCtx->streams[VideoIndex]->avg_frame_rate.den;VideoCtrl.RefreshTime /= pFormatCtx->streams[VideoIndex]->avg_frame_rate.num;}printf("VideoCtrl.RefreshTime:%d\n", VideoCtrl.RefreshTime);}else{printf("Didn't find a video stream.\n");}if (AudioIndex != -1){	//准备音频的解码操作上下文数据结构，// pAudioCodecCtx = pFormatCtx->streams[AudioIndex]->codec;	pAudioCodec = avcodec_find_decoder(pFormatCtx->streams[AudioIndex]->codecpar->codec_id);pAudioCodecCtx = avcodec_alloc_context3(pAudioCodec);pAudioCodecParameters = pFormatCtx->streams[AudioIndex]->codecpar;avcodec_parameters_to_context(pAudioCodecCtx, pAudioCodecParameters);if (pAudioCodec == NULL){printf("Audio Codec not found.\n");return -1;}if (avcodec_open2(pAudioCodecCtx, pAudioCodec, NULL) < 0){printf("Could not open audio codec.\n");return -1;}// prepare Out Audio ParamAudioOutChannelLayout = AV_CH_LAYOUT_STEREO;out_nb_samples = pAudioCodecCtx->frame_size * 2;	//nb_samples: AAC-1024 MP3-1152out_sample_fmt = AV_SAMPLE_FMT_S16;out_sample_rate = pAudioCodecCtx->sample_rate * 2;// 此处一定使用pAudioCodecCtx->sample_rate这个变量赋值，否则使用不一样的值会造成音频少采样或者过采样，导致音频播放出现杂音out_channels = av_get_channel_layout_nb_channels(AudioOutChannelLayout);out_buffer_size = av_samples_get_buffer_size(NULL, out_channels, out_nb_samples, out_sample_fmt, 1);//mp3:out_nb_samples:1152, out_channels:2, out_buffer_size:4608, pCodecCtx->channels:2//aac:out_nb_samples:1024, out_channels:2, out_buffer_size:4096, pCodecCtx->channels:2printf("out_nb_samples:%d, out_channels:%d, out_buffer_size:%d, pCodecCtx->channels:%d\n",out_nb_samples, out_channels, out_buffer_size, pAudioCodecCtx->channels);pAudioOutBuffer = (uint8_t *)av_malloc(MAX_AUDIO_FRAME_SIZE * 2);//FIX:Some Codec's Context Information is missingint64_t in_channel_layout = av_get_default_channel_layout(pAudioCodecCtx->channels);//SwrAudioConvertCtx = swr_alloc();AudioConvertCtx = swr_alloc_set_opts(AudioConvertCtx, AudioOutChannelLayout,out_sample_fmt, out_sample_rate,in_channel_layout, pAudioCodecCtx->sample_fmt,pAudioCodecCtx->sample_rate, 0, NULL);swr_init(AudioConvertCtx);AudioCtrl.pFormatCtx = pFormatCtx;AudioCtrl.pStream = pFormatCtx->streams[AudioIndex];AudioCtrl.pCodec = pAudioCodec;// AudioCtrl.pCodecCtx = pFormatCtx->streams[AudioIndex]->codec;pAudioCodecParameters = pFormatCtx->streams[AudioIndex]->codecpar;AVCodecContext *pAudioCodecContext = avcodec_alloc_context3(NULL);avcodec_parameters_to_context(pAudioCodecContext, pAudioCodecParameters);AudioCtrl.pCodecCtx = pAudioCodecContext;AudioCtrl.pConvertCtx = AudioConvertCtx;AudioCtrl.AudioOutChannelLayout = AudioOutChannelLayout;AudioCtrl.out_nb_samples = out_nb_samples;AudioCtrl.out_sample_fmt = out_sample_fmt;AudioCtrl.out_sample_rate = out_sample_rate;AudioCtrl.out_channels = out_channels;AudioCtrl.out_buffer_size = out_buffer_size;AudioCtrl.pAudioOutBuffer = pAudioOutBuffer;AudioCtrl.AudioIndex = AudioIndex;}else{printf("Didn't find a audio stream.\n");}//Output Info-----------------------------printf("---------------- File Information ---------------\n");av_dump_format(pFormatCtx, 0, filepath, 0);printf("-------------- File Information end -------------\n");if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)){printf("Could not initialize SDL - %s\n", SDL_GetError());return -1;}if (VideoIndex != -1){//SDL 2.0 Support for multiple windows//SDL_VideoSpecVideoCtrl.screen_w = pVideoCodecCtx->width;VideoCtrl.screen_h = pVideoCodecCtx->height;VideoCtrl.screen = SDL_CreateWindow("Simplest ffmpeg player's Window", SDL_WINDOWPOS_UNDEFINED,SDL_WINDOWPOS_UNDEFINED, VideoCtrl.screen_w, VideoCtrl.screen_h, SDL_WINDOW_OPENGL);if (!VideoCtrl.screen){printf("SDL: could not create window - exiting:%s\n", SDL_GetError());return -1;}VideoCtrl.sdlRenderer = SDL_CreateRenderer(VideoCtrl.screen, -1, 0);//IYUV: Y + U + V  (3 planes)//YV12: Y + V + U  (3 planes)VideoCtrl.sdlTexture = SDL_CreateTexture(VideoCtrl.sdlRenderer, SDL_PIXELFORMAT_IYUV, SDL_TEXTUREACCESS_STREAMING,pVideoCodecCtx->width, pVideoCodecCtx->height);VideoCtrl.sdlRect.x = 0;VideoCtrl.sdlRect.y = 0;VideoCtrl.sdlRect.w = VideoCtrl.screen_w;VideoCtrl.sdlRect.h = VideoCtrl.screen_h;VideoCtrl.video_tid = SDL_CreateThread(video_refresh_thread, NULL, NULL);ret = pthread_create(&video_tid, NULL, thread_video, &VideoCtrl);if (ret){printf("create thr_rvs video thread failed, error = %d \n", ret);return -1;}}if (AudioIndex != -1){//SDL_AudioSpecSDL_AudioSpec AudioSpec;AudioSpec.freq = out_sample_rate;AudioSpec.format = AUDIO_S16SYS;AudioSpec.channels = out_channels;AudioSpec.silence = 0;AudioSpec.samples = out_nb_samples;AudioSpec.callback = fill_audio;AudioSpec.userdata = (void*)&AudioCtrl;if (SDL_OpenAudio(&AudioSpec, NULL) < 0){printf("can't open audio.\n");return -1;}ret = pthread_create(&audio_tid, NULL, thread_audio, &AudioCtrl);if (ret){printf("create thr_rvs video thread failed, error = %d \n", ret);return -1;}SDL_PauseAudio(0);}SDL_Thread *event_tid;event_tid = SDL_CreateThread(SDL_event_thread, NULL, NULL);VideoCnt = 0;AudioCnt = 0;Packet = (AVPacket *)av_malloc(sizeof(AVPacket));av_init_packet(Packet);while (1){if (thread_pause){if ((CurKeyProcess == 0) && video_pause && audio_pause){switch (CurKeyCode){case SDLK_RIGHT://DstAudioDts = CurAudioDts + (int64_t) (3 / av_q2d(AudioCtrl.pStream->time_base));//因为time_base分数结构中，num基本都为1，因此为了减少浮点数乘除法，可以直接乘以time_base的分母DstAudioDts = CurAudioDts + 3 * AudioCtrl.pStream->time_base.den;DstVideoDts = CurVideoDts + 3 * VideoCtrl.pStream->time_base.den;ret = av_seek_frame(pFormatCtx, AudioIndex, DstAudioDts, AVSEEK_FLAG_FRAME);//ret = av_seek_frame(pFormatCtx, VideoIndex, DstVideoDts, AVSEEK_FLAG_FRAME);printf("SDLK_RIGHT av_seek_frame ret = %d, CurAudioDts:%ld, CurVideoDts:%ld, DstVideoDts:%ld, DstAudioDts:%ld\n",ret, CurAudioDts, CurVideoDts, DstVideoDts, DstAudioDts);avcodec_flush_buffers(AudioCtrl.pCodecCtx);avcodec_flush_buffers(VideoCtrl.pCodecCtx);PacketArrayClear(&VideoCtrl.Video);PacketArrayClear(&AudioCtrl.Audio);break;case SDLK_LEFT:DstAudioDts = CurAudioDts - 3 * AudioCtrl.pStream->time_base.den;DstVideoDts = CurVideoDts - 3 * VideoCtrl.pStream->time_base.den;if (DstAudioDts < 0) DstAudioDts = 0;if (DstVideoDts < 0) DstVideoDts = 0;ret = av_seek_frame(pFormatCtx, AudioIndex, DstAudioDts, AVSEEK_FLAG_BACKWARD | AVSEEK_FLAG_FRAME);//ret = av_seek_frame(pFormatCtx, VideoIndex, DstVideoDts, AVSEEK_FLAG_BACKWARD | AVSEEK_FLAG_FRAME);printf("SDLK_LEFT av_seek_frame ret = %d, CurAudioDts:%ld, CurVideoDts:%ld, DstVideoDts:%ld, DstAudioDts:%ld\n",ret, CurAudioDts, CurVideoDts, DstVideoDts, DstAudioDts);avcodec_flush_buffers(AudioCtrl.pCodecCtx);avcodec_flush_buffers(VideoCtrl.pCodecCtx);PacketArrayClear(&VideoCtrl.Video);PacketArrayClear(&AudioCtrl.Audio);break;default:break;}CurKeyProcess = 1;thread_pause = !thread_pause;}Sleep(10000);continue;}if (av_read_frame(pFormatCtx, Packet) < 0){//			thread_exit = 1;//			SDL_Event event;//			event.type = SFM_BREAK_EVENT;//			SDL_PushEvent(&event);//			printf("---------> av_read_frame < 0, thread_exit = 1  !!!\n");//			break;av_seek_frame(pFormatCtx, AudioIndex, 0, AVSEEK_FLAG_BACKWARD | AVSEEK_FLAG_FRAME);continue;}if (Packet->stream_index == VideoIndex){if (VideoCtrl.Video.wIndex >= PACKET_ARRAY_SIZE){VideoCtrl.Video.wIndex = 0;}while (IsPacketArrayFull(&VideoCtrl.Video)){Sleep(5000);//printf("---------> VideoCtrl.Video.PacketArray FULL !!!\n");}i = VideoCtrl.Video.wIndex;VideoCtrl.Video.PacketArray[i].Packet = *Packet;VideoCtrl.Video.PacketArray[i].dts = Packet->dts;VideoCtrl.Video.PacketArray[i].pts = Packet->pts;VideoCtrl.Video.PacketArray[i].state = 1;VideoCtrl.Video.wIndex++;//printf("VideoCtrl packet put,dts:%ld, pts:%ld, VideoCnt:%d\n", Packet->dts, Packet->pts, VideoCnt++);}if (Packet->stream_index == AudioIndex){if (AudioCtrl.Audio.wIndex >= PACKET_ARRAY_SIZE){AudioCtrl.Audio.wIndex = 0;}while (IsPacketArrayFull(&AudioCtrl.Audio)){Sleep(5000);//printf("---------> AudioCtrl.Audio.PacketArray FULL !!!\n");}i = AudioCtrl.Audio.wIndex;AudioCtrl.Audio.PacketArray[i].Packet = *Packet;AudioCtrl.Audio.PacketArray[i].dts = Packet->dts;AudioCtrl.Audio.PacketArray[i].pts = Packet->pts;AudioCtrl.Audio.PacketArray[i].state = 1;AudioCtrl.Audio.wIndex++;//printf("AudioCtrl.frame_put, AudioCnt:%d\n", AudioCnt++);}if (thread_exit) break;}SDL_WaitThread(event_tid, NULL);SDL_WaitThread(VideoCtrl.video_tid, NULL);pthread_join(audio_tid, NULL);pthread_join(video_tid, NULL);SDL_CloseAudio();//Close SDLSDL_Quit();swr_free(&AudioConvertCtx);sws_freeContext(VideoConvertCtx);av_free(pVideoOutBuffer);avcodec_close(pVideoCodecCtx);av_free(pAudioOutBuffer);avcodec_close(pAudioCodecCtx);avformat_close_input(&pFormatCtx);return 0;
}