ffmpeg SDL2.0播放音频

参考文章：http://blog.csdn.net/leixiaohua1020/article/details/10528443

#include 
#include 
extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswresample/swresample.h"
//SDL
#include "SDL.h"
#include "SDL_thread.h"
};

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


//Output PCM
#define OUTPUT_PCM 0
//Use SDL
#define USE_SDL 1

//Buffer:
//|-----------|-------------|
//chunk-------pos---len-----|
static  Uint8  *audio_chunk; 
static  Uint32  audio_len; 
static  Uint8  *audio_pos; 


void  fill_audio(void *udata,Uint8 *stream,int len){ 
	SDL_memset(stream,0,len);// necessary
	 
	if(audio_len==0)		  
			return; 
	len=(len>audio_len?audio_len:len);	  

	SDL_MixAudio(stream,audio_pos,len,SDL_MIX_MAXVOLUME);
	audio_pos += len; 
	audio_len -= len; 
} 
//-----------------
 
int main(int argc, char* argv[])
{
	AVFormatContext	*pFormatCtx;
	int				i, audioStream;
	AVCodecContext	*pCodecCtx;
	AVCodec			*pCodec;


	char url[]="1.mp3";
	av_register_all();
	avformat_network_init();
	pFormatCtx = avformat_alloc_context();
	//Open
	if(avformat_open_input(&pFormatCtx,url,NULL,NULL)!=0){
		printf("Couldn't open input stream.\n");
		return -1;
	}
	// Retrieve stream information
	if(avformat_find_stream_info(pFormatCtx,NULL)<0){
		printf("Couldn't find stream information.\n");
		return -1;
	}
	// Dump valid information onto standard error
	av_dump_format(pFormatCtx, 0, url, false);

	// Find the first audio stream
	audioStream=-1;
	for(i=0; i < pFormatCtx->nb_streams; i++)
		if(pFormatCtx->streams[i]->codecpar->codec_type==AVMEDIA_TYPE_AUDIO){
			audioStream=i;
			break;
		}

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

	// Get a pointer to the codec context for the audio stream
	pCodecCtx=avcodec_alloc_context3(NULL);
	avcodec_parameters_to_context(pCodecCtx,pFormatCtx->streams[audioStream]->codecpar);
	//pCodecCtx=pFormatCtx->streams[audioStream]->codec;

	// Find the decoder for the audio stream
	pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
	if(pCodec==NULL){
		printf("Codec not found.\n");
		return -1;
	}

	// Open codec
	if(avcodec_open2(pCodecCtx, pCodec,NULL)<0){
		printf("Could not open codec.\n");
		return -1;
	}

	FILE *pFile=NULL;
#if OUTPUT_PCM
	pFile=fopen("output.pcm", "wb");
#endif

	AVPacket *packet=(AVPacket *)malloc(sizeof(AVPacket));
	av_init_packet(packet);

	//Out Audio Param
	uint64_t out_channel_layout=AV_CH_LAYOUT_STEREO;
	int out_nb_samples=1024;
	AVSampleFormat out_sample_fmt=AV_SAMPLE_FMT_S16;
	int out_sample_rate=44100;
	int out_channels=av_get_channel_layout_nb_channels(out_channel_layout);
	//Out Buffer Size
	int out_buffer_size=av_samples_get_buffer_size(NULL,out_channels ,out_nb_samples,out_sample_fmt, 1);

	uint8_t *out_buffer=(uint8_t *)av_malloc(MAX_AUDIO_FRAME_SIZE*2);

	AVFrame	*pFrame;
	pFrame=av_frame_alloc();
//SDL------------------
#if USE_SDL
	//Init
	if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {  
		printf( "Could not initialize SDL - %s\n", SDL_GetError()); 
		return -1;
	}
	//SDL_AudioSpec
	SDL_AudioSpec wanted_spec;
	wanted_spec.freq = out_sample_rate; 
	wanted_spec.format = AUDIO_S16SYS; 
	wanted_spec.channels = out_channels; 
	wanted_spec.silence = 0; 
	wanted_spec.samples = out_nb_samples; 
	wanted_spec.callback = fill_audio; 
	wanted_spec.userdata = pCodecCtx; 

	if (SDL_OpenAudio(&wanted_spec, NULL)<0){ 
		printf("can't open audio.\n"); 
		return -1; 
	} 
#endif
	printf("Bitrate:\t %3d\n", pFormatCtx->bit_rate);
	printf("Decoder Name:\t %s\n", pCodecCtx->codec->long_name);
	printf("Channels:\t %d\n", pCodecCtx->channels);
	printf("Sample per Second\t %d \n", pCodecCtx->sample_rate);

	uint32_t ret,len = 0;
	int got_picture;
	int index = 0;
	//FIX:Some Codec's Context Information is missing
	int64_t in_channel_layout=av_get_default_channel_layout(pCodecCtx->channels);
	//Swr
	struct SwrContext *au_convert_ctx;
	au_convert_ctx = swr_alloc();
	au_convert_ctx=swr_alloc_set_opts(au_convert_ctx,out_channel_layout, out_sample_fmt, out_sample_rate,
		in_channel_layout,pCodecCtx->sample_fmt , pCodecCtx->sample_rate,0, NULL);
	swr_init(au_convert_ctx);
	while(av_read_frame(pFormatCtx, packet)>=0){
		if(packet->stream_index==audioStream){

			//ret = avcodec_decode_audio4( pCodecCtx, pFrame,&got_picture, packet);
			ret = avcodec_send_packet(pCodecCtx,packet);
			if ( ret < 0 ) {
                printf("Error in decoding audio frame.\n");
                return -1;
            }
			ret = avcodec_receive_frame(pCodecCtx,pFrame);
			if(ret== AVERROR(EAGAIN) || ret==AVERROR_EOF)
							continue;
			else if(ret<0)
			{
				exit(-1);
			}
			if ( true ){
				swr_convert(au_convert_ctx,&out_buffer, MAX_AUDIO_FRAME_SIZE,(const uint8_t **)pFrame->data , pFrame->nb_samples);
				if(wanted_spec.samples!=pFrame->nb_samples){
					SDL_CloseAudio();
					out_nb_samples=pFrame->nb_samples;
					out_buffer_size=av_samples_get_buffer_size(NULL,out_channels ,out_nb_samples,out_sample_fmt, 1);
					wanted_spec.samples=out_nb_samples;
					SDL_OpenAudio(&wanted_spec, NULL);
				}

#if OUTPUT_PCM
				//Write PCM
				fwrite(out_buffer, 1, out_buffer_size, pFile);
#endif
				
				index++;
			}
//SDL------------------
#if USE_SDL
			//Set audio buffer (PCM data)
			audio_chunk = (Uint8 *) out_buffer; 
			//Audio buffer length
			audio_len =out_buffer_size;

			audio_pos = audio_chunk;
			//Play
			SDL_PauseAudio(0);
			while(audio_len>0)//Wait until finish
				SDL_Delay(1); 
#endif
		}
		av_packet_unref(packet);
	}

	swr_free(&au_convert_ctx);

#if USE_SDL
	SDL_CloseAudio();//Close SDL
	SDL_Quit();
#endif
	// Close file
#if OUTPUT_PCM
	fclose(pFile);
#endif
	av_free(out_buffer);
	// Close the codec
	avcodec_close(pCodecCtx);
	// Close the video file
	avformat_close_input(&pFormatCtx);

	return 0;
}