FFmpeg音视频播放器系列（开篇）

简介

学习FFmpeg已经有一段时间了，都是断断续续、零零散散的，没有系统的总结过，为了保证学习效果，决定自己写一个音视频播放器，借着这个项目对FFmpeg进行系统的学习与总结，争取对FFmpeg达到熟练应用的程度。
FFmpeg音视频播放器系列，本着循序渐进的过程，先从最简单的开始，逐步深入到使用QT写出一个带有GUI界面的应用软件。这个项目估计要耗时很长，但愿自己能坚持下来。
先对这个项目确定一个小目标吧：
1、模仿市面上的播放器界面使用QT完成GUI
2、可以选择单独播放视频或者音频
3、可以播放网络视频流
4、可以录制音频与视频
5、可以播放摄像头视频
好了，就这么多，多了怕自己完成不了。
自己的开发平台如下：
Ubuntu16.04
FFmpeg：4.0.2
SDL2：2.0.8
QT：5.12.1

FFmpeg的学习我基本上是基于雷神的博客，再次他致敬！他的FFmpeg博客地址在此先行贴出：
https://blog.csdn.net/leixiaohua1020/column/info/ffmpeg-devel

FFMPEG+SDL的视频播放器

雷神也有这篇博客，不过他是将视频与音频分开的，带有音频的视频在播放时，只能播放视频而没有声音，因此本篇就先进行一下综合，写出一个基于FFMPEG+SDL的简单视频播放器，可以同时播放音频与视频，可能会有音视频播放同步的问题，待到下一篇进行总结与说明。

代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define __STDC_CONSTANT_MACROS

//Linux...
#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>
#ifdef __cplusplus
};
#endif


#define MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

static  Uint8  *audio_chunk;
static  Sint32  audio_len;
static  Uint8  *audio_pos;


//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 sfp_refresh_thread(void *opaque){
	thread_exit=0;
	thread_pause=0;

	while (!thread_exit)
	{
		if(!thread_pause)
		{
			SDL_Event event;
			event.type = SFM_REFRESH_VIDEO_EVENT;
			SDL_PushEvent(&event);
		}
		SDL_Delay(40);
	}
	thread_exit=0;
	thread_pause=0;
	//Break
	SDL_Event event;
	event.type = SFM_BREAK_EVENT;
	SDL_PushEvent(&event);

	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){
	//SDL 2.0
	SDL_memset(stream, 0, len);
	if(audio_len==0)
		return;

	len=(len>audio_len?audio_len:len);	/*  Mix  as  much  data  as  possible  */

	SDL_MixAudio(stream, audio_pos, len, SDL_MIX_MAXVOLUME);
	audio_pos += len;
	audio_len -= len;
}



int main(int argc, char* argv[])
{
	AVFormatContext	*pFormatCtx;
	AVCodecContext	*pVideoCodecCtx, *pAudioCodecCtx;
	AVCodec			*pVideoCodec, *pAudioCodec;
	AVFrame			*pVideoFrame,*pAudioFrame,*pFrameYUV;
	unsigned char 	*pVideoOutBuffer, *pAudioOutBuffer;
	//AVPacket 		*pVideoPacket, *pAudioPacket;
	AVPacket 		*Packet;
	int 			i, ret, GotVideoPicture, GotAudioPicture;
	int 			audioCnt, videoCnt;

	//------------SDL----------------
	int screen_w,screen_h;
	SDL_Window *screen;
	SDL_Renderer* sdlRenderer;
	SDL_Texture* sdlTexture;
	SDL_Rect sdlRect;
	SDL_Thread *video_tid;
	SDL_Event event;

	struct SwsContext *VideoConvertCtx;
	struct SwrContext *AudioConvertCtx;
	int VideoIndex;
	int AudioIndex;

	char *filepath = argv[1];

	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]->codec->codec_type==AVMEDIA_TYPE_VIDEO)
		{
			VideoIndex = i;
			printf("video AVRational.num:%d, AVRational.den:%d,\n",
					pFormatCtx->streams[VideoIndex]->time_base.num,
					pFormatCtx->streams[VideoIndex]->time_base.den);
		}

		if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO)
		{
			AudioIndex = i;
			printf("audio AVRational.num:%d, AVRational.den:%d,\n",
					pFormatCtx->streams[AudioIndex]->time_base.num,
					pFormatCtx->streams[AudioIndex]->time_base.den);
		}
	}

	if(VideoIndex == -1)
	{
		printf("Didn't find a video stream.\n");
		return -1;
	}

	if(AudioIndex == -1)
	{
		printf("Didn't find a audio stream.\n");
		return -1;
	}

	pVideoCodecCtx = pFormatCtx->streams[VideoIndex]->codec;
	pVideoCodec = avcodec_find_decoder(pVideoCodecCtx->codec_id);
	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;
	}

	pAudioCodecCtx = pFormatCtx->streams[AudioIndex]->codec;
	pAudioCodec = avcodec_find_decoder(pAudioCodecCtx->codec_id);
	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 video
	pVideoFrame = av_frame_alloc();
	pFrameYUV = av_frame_alloc();

	i = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pVideoCodecCtx->width, pVideoCodecCtx->height, 1);
	pVideoOutBuffer = (unsigned char *)av_malloc(i);
	av_image_fill_arrays(pFrameYUV->data, 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);

	// prepare audio

	//Out Audio Param
	uint64_t AudioOutChannelLayout  = AV_CH_LAYOUT_STEREO;
	//nb_samples: AAC-1024 MP3-1152
	int out_nb_samples 				= pAudioCodecCtx->frame_size;
	AVSampleFormat out_sample_fmt 	= AV_SAMPLE_FMT_S16;
	int out_sample_rate				= pAudioCodecCtx->sample_rate;
	int out_channels				= av_get_channel_layout_nb_channels(AudioOutChannelLayout);
	//Out Buffer Size
	int out_buffer_size				= av_samples_get_buffer_size(NULL,out_channels ,out_nb_samples,out_sample_fmt, 1);

	//out_nb_samples:1152, out_channels:2, out_buffer_size:4608, pCodecCtx->channels:2
	printf("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);
	pAudioFrame						= av_frame_alloc();

	//FIX:Some Codec's Context Information is missing
	int64_t in_channel_layout		= av_get_default_channel_layout(pAudioCodecCtx->channels);
	//Swr
	AudioConvertCtx 				= 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);

	//Output Info-----------------------------
	printf("---------------- File Information ---------------\n");
	av_dump_format(pFormatCtx, 0, filepath, 0);
	printf("-------------------------------------------------\n");

	if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER))
	{
		printf( "Could not initialize SDL - %s\n", SDL_GetError());
		return -1;
	}

	//SDL 2.0 Support for multiple windows
	//SDL_VideoSpec
	screen_w = pVideoCodecCtx->width;
	screen_h = pVideoCodecCtx->height;
	screen = SDL_CreateWindow("Simplest ffmpeg player's Window", SDL_WINDOWPOS_UNDEFINED,
							  SDL_WINDOWPOS_UNDEFINED, screen_w, screen_h, SDL_WINDOW_OPENGL);

	if(!screen)
	{
		printf("SDL: could not create window - exiting:%s\n",SDL_GetError());
		return -1;
	}
	sdlRenderer = SDL_CreateRenderer(screen, -1, 0);
	//IYUV: Y + U + V  (3 planes)
	//YV12: Y + V + U  (3 planes)
	sdlTexture = SDL_CreateTexture(sdlRenderer, SDL_PIXELFORMAT_IYUV, SDL_TEXTUREACCESS_STREAMING,
								   pVideoCodecCtx->width, pVideoCodecCtx->height);

	sdlRect.x=0;
	sdlRect.y=0;
	sdlRect.w=screen_w;
	sdlRect.h=screen_h;

	//SDL_AudioSpec
	SDL_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 	= pAudioCodecCtx;

	if (SDL_OpenAudio(&AudioSpec, NULL) < 0)
	{
		printf("can't open audio.\n");
		return -1;
	}

	//pAudioPacket = (AVPacket *)av_malloc(sizeof(AVPacket));
	//pVideoPacket = (AVPacket *)av_malloc(sizeof(AVPacket));
	Packet = (AVPacket *)av_malloc(sizeof(AVPacket));
	av_init_packet(Packet);

	index = 0;
	audioCnt = 0;
	videoCnt = 0;
	video_tid = SDL_CreateThread(sfp_refresh_thread, NULL, NULL);
	SDL_PauseAudio(0);

	while(1)
	{
		if(av_read_frame(pFormatCtx, Packet) < 0)
		{
			thread_exit = 1;
			break;
		}
		if(Packet->stream_index == VideoIndex)
		{
			//printf("get video -------------> count:%d\n", videoCnt);
			ret = avcodec_decode_video2(pVideoCodecCtx, pVideoFrame, &GotVideoPicture, Packet);
			if(ret < 0)
			{
				printf("Video Decode Error.\n");
				return -1;
			}
			if(GotVideoPicture)
			{	
				sws_scale(VideoConvertCtx, (const unsigned char* const*)pVideoFrame->data,
						  pVideoFrame->linesize, 0, pVideoCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);
				printf("Video cnt:%5d\t pts:%ld\t packet size:%d, pFrame->nb_samples:%d\n",
						videocnt, Packet->pts, Packet->size, pVideoFrame->nb_samples);
				//SDL---------------------------
				SDL_UpdateTexture( sdlTexture, NULL, pFrameYUV->data[0], pFrameYUV->linesize[0] );
				SDL_RenderClear( sdlRenderer );
				//SDL_RenderCopy( sdlRenderer, sdlTexture, &sdlRect, &sdlRect );
				SDL_RenderCopy( sdlRenderer, sdlTexture, NULL, NULL);
				SDL_RenderPresent( sdlRenderer );
				SDL_Delay(40);
				videocnt++;
				//SDL End-----------------------
			}
		}

		if(Packet->stream_index == AudioIndex)
		{
			//printf("get audio count:%d\n", audioCnt);
			ret = avcodec_decode_audio4( pAudioCodecCtx, pAudioFrame,&GotAudioPicture, Packet);
			if ( ret < 0 )
			{
				printf("Error in decoding audio frame.\n");
				return -1;
			}
			if ( GotAudioPicture > 0 )
			{
				swr_convert(AudioConvertCtx,&pAudioOutBuffer, MAX_AUDIO_FRAME_SIZE,
						(const uint8_t **)pAudioFrame->data , pAudioFrame->nb_samples);
				printf("Auduo cnt:%5d\t pts:%ld\t packet size:%d, pFrame->nb_samples:%d\n",
						audiocnt, Packet->pts, Packet->size, pAudioFrame->nb_samples);

				audiocnt++;
			}

			while(audio_len > 0)//Wait until finish
				SDL_Delay(1);

			//Set audio buffer (PCM data)
			audio_chunk = (Uint8 *) pAudioOutBuffer;
			//Audio buffer length
			audio_len = out_buffer_size;
			audio_pos = audio_chunk;
		}
		av_free_packet(Packet);
//		SDL_WaitEvent(&event);
//		if(event.type == SFM_REFRESH_VIDEO_EVENT)
//		{
//
//		}
//		else if(event.type == SDL_KEYDOWN)
//		{
//			//Pause
//			if(event.key.keysym.sym == SDLK_SPACE)
//			{
//				thread_pause = !thread_pause;
//				printf("video got pause event!\n");
//			}
//		}
//		else if(event.type == SDL_QUIT)
//		{
//			thread_exit = 1;
//		}
//		else if(event.type==SFM_BREAK_EVENT)
//		{
//			break;
//		}
	}

	swr_free(&AudioConvertCtx);
	sws_freeContext(VideoConvertCtx);

	av_free(pVideoOutBuffer);
	av_frame_free(&pFrameYUV);
	av_frame_free(&pVideoFrame);
	avcodec_close(pVideoCodecCtx);

	SDL_CloseAudio();//Close SDL
	SDL_Quit();

	av_free(pAudioOutBuffer);
	av_frame_free(&pAudioFrame);
	avcodec_close(pAudioCodecCtx);
	avformat_close_input(&pFormatCtx);
}

makefile

TARGET		 = ffmpeg_sdl2_av_play
LIB_PATH 	 = /usr/local/lib/
 
FFMPEG_LIBS = -lavutil -lavdevice -lavformat -lavcodec -lswresample -lavfilter -lswscale 
SDL_LIBS	= -lSDL2
EXTRA_LIBS  = -lz -lm -lpthread -lstdc++ -lm -lrt -lpcre
ALL_LIBS	= $(EXTRA_LIBS) $(SDL_LIBS) $(FFMPEG_LIBS)  
 
COMPILE_OPTS = -v -g -Wall -Wno-deprecated-declarations 

C_COMPILER   = g++
C_FLAGS 	 = $(CFLAGS) $(COMPILE_OPTS) 
LD_FLAGS 	 = -L$(LIB_PATH) $(LDFLAGS)

SRC = ffmpeg_sdl2_av_play.cpp

ALL:
	$(C_COMPILER) $(C_FLAGS) $(LD_FLAGS) $(SRC) -o $(TARGET) $(ALL_LIBS) 
clean:
	rm -rf $(TARGET) *.o *.mp4 *.wav *.h264 *.avi *.flv 

问题

以上代码不可避免的出现了音视频播放同步的问题，经过短暂的研究，发现发现播放同步内容也不少，因此就在下一篇解决音视频播放同步的问题，并总结同步的原理，与解决的方法。
下一篇将研究如何根据文件信息，获取视频帧率，音频信息，时间戳pts信息等，然后说明如何进行音视频播放同步。