二、基于FFmpeg和SDL的音乐播放器

缅怀雷大神：https://blog.csdn.net/leixiaohua1020/article/details/38868499

一、 声明头文件

由于FFmpeg和SDL使用纯C来实现的，我们需要声明用C来编译

extern "C"
{
	//封装格式
#include "libavformat/avformat.h"
	//解码
#include "libavcodec/avcodec.h"
	//缩放
#include "libswscale/swscale.h"
#include "libswresample/swresample.h"    //声音文件使用
#include "libavutil/imgutils.h"          //播放图像使用
	//播放
#include "SDL2/SDL.h"
};

二、 注册组件以初始化

av_register_all();
avformat_network_init();
pFormatCtx = avformat_alloc_context();
if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER))
{
	printf("Could not initialize SDL - %s\n", SDL_GetError());
}

三、 打开文件并且获取解码器

filepath：文件路径("test.mp3")

type：数据流类型(音频：AVMEDIA_TYPE_AUDIO)

//打开输入文件
	if (avformat_open_input(&pFormatCtx, filepath, NULL, NULL) != 0){
		printf("Couldn't open input stream.\n");
		return -1;
	}
	//获取文件信息
	if (avformat_find_stream_info(pFormatCtx, NULL)<0){
		printf("Couldn't find stream information.\n");
		return -1;
	}
	//找到对应的type所在的pFormatCtx->streams的索引位置
	index = -1;
	for (int i = 0; inb_streams; i++)
		if (pFormatCtx->streams[i]->codec->codec_type == type){
			index = i;
			break;
		}
	if (index == -1){
		printf("Didn't find a video stream.\n");
		return -1;
	}
	//获取解码器
	pCodeCtx = pFormatCtx->streams[index]->codec;
	pCodec = avcodec_find_decoder(pCodeCtx->codec_id);
	if (pCodec == NULL){
		printf("Codec not found.\n");
		return -1;
	}
	//打开解码器
	if (avcodec_open2(pCodeCtx, pCodec, NULL)<0){
		printf("Could not open codec.\n");
		return -1;
	}

四、音频采样设置

//重采样设置选项-----------------------------------------------------------start
	//输入的采样格式
	in_sample_fmt = pCodeCtx->sample_fmt;
	//输出的采样格式 16bit PCM
	out_sample_fmt = AV_SAMPLE_FMT_S16;
	//输入的采样率
	in_sample_rate = pCodeCtx->sample_rate;
	//输出的采样率
	out_sample_rate = 44100;
	//输入的声道布局
	in_ch_layout = pCodeCtx->channel_layout;
	if (in_ch_layout <= 0)
	{
		in_ch_layout = av_get_default_channel_layout(pCodeCtx->channels);
	}
	//输出的声道布局
	out_ch_layout = AV_CH_LAYOUT_MONO;

	//frame->16bit 44100 PCM 统一音频采样格式与采样率
	swrCtx = swr_alloc();
	swr_alloc_set_opts(swrCtx, out_ch_layout, out_sample_fmt, out_sample_rate, in_ch_layout, in_sample_fmt,
		in_sample_rate, 0, NULL);
	swr_init(swrCtx);
	//重采样设置选项-----------------------------------------------------------end

五、SDL播放设置

注意：使用回调函数进行播放

回调函数：

static Uint8 *audio_chunk;
//设置音频数据长度
static Uint32 audio_len;
static Uint8 *audio_pos;
void fill_audio(void *udata, Uint8 *stream, int len){
	//SDL 2.0
	SDL_memset(stream, 0, len);
	if (audio_len == 0)		//有数据才播放
		return;
	len = (len>audio_len ? audio_len : len);	

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

//获取输出的声道个数
	out_channel_nb = av_get_channel_layout_nb_channels(out_ch_layout);
	//SDL_AudioSpec
	wanted_spec.freq = out_sample_rate;
	wanted_spec.format = AUDIO_S16SYS;
	wanted_spec.channels = out_channel_nb;
	wanted_spec.silence = 0;
	wanted_spec.samples = pCodeCtx->frame_size;
	wanted_spec.callback = fill_audio;//回调函数
	wanted_spec.userdata = pCodeCtx;
	if (SDL_OpenAudio(&wanted_spec, NULL)<0){
		printf("can't open audio.\n");
		return -1;
	}

 

六、读取数据并播放

//编码数据
	AVPacket *packet = (AVPacket *)av_malloc(sizeof(AVPacket));
	//解压缩数据
	AVFrame *frame = av_frame_alloc();
	//存储pcm数据
	uint8_t *out_buffer = (uint8_t *)av_malloc(2 * 44100);

	int ret, got_frame, framecount = 0;
	//一帧一帧读取压缩的音频数据AVPacket
	while (1)
	while (av_read_frame(pFormatCtx, packet) >= 0) {
		if (packet->stream_index == index) {
			//解码AVPacket->AVFrame
			ret = avcodec_decode_audio4(pCodeCtx, frame, &got_frame, packet);
			if (ret < 0) {
				printf("%s", "解码完成");
			}
			//非0，正在解码
			int out_buffer_size;
			if (got_frame) {
				//printf("解码%d帧", framecount++);
				swr_convert(swrCtx, &out_buffer, 2 * 44100, (const uint8_t **)frame->data, frame->nb_samples);
				//获取sample的size
				out_buffer_size = av_samples_get_buffer_size(NULL, out_channel_nb, frame->nb_samples,
					out_sample_fmt, 1);
				//设置音频数据缓冲,PCM数据
				audio_chunk = (Uint8 *)out_buffer;
				//设置音频数据长度
				audio_len = out_buffer_size;
				audio_pos = audio_chunk;
				//回放音频数据 
				SDL_PauseAudio(0);
				while (audio_len>0)//等待直到音频数据播放完毕! 
					SDL_Delay(10);

				packet->data += ret;
				packet->size -= ret;
			}
		}
	}

七、完整代码

extern "C"
{
	//封装格式
#include "libavformat/avformat.h"
	//解码
#include "libavcodec/avcodec.h"
	//缩放
#include "libswscale/swscale.h"
#include "libswresample/swresample.h"
#include "libavutil/imgutils.h"
	//播放
#include "SDL2/SDL.h"
};

static Uint8 *audio_chunk;
//设置音频数据长度
static Uint32 audio_len;
static Uint8 *audio_pos;
void fill_audio(void *udata, Uint8 *stream, int len){
	//SDL 2.0
	SDL_memset(stream, 0, len);
	if (audio_len == 0)		//有数据才播放
		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;
	AVCodecContext	*pCodeCtx;
	AVCodec			*pCodec;
	int index;
	SwrContext *swrCtx;

	//重采样设置选项-----------------------------------------------------------start
	//输入的采样格式
	enum AVSampleFormat in_sample_fmt;
	//输出的采样格式 16bit PCM
	enum AVSampleFormat out_sample_fmt;
	//输入的采样率
	int in_sample_rate;
	//输出的采样率
	int out_sample_rate;
	//输入的声道布局
	uint64_t in_ch_layout;
	//输出的声道布局
	uint64_t out_ch_layout;
	//重采样设置选项-----------------------------------------------------------end
	//SDL_AudioSpec
	SDL_AudioSpec wanted_spec;
	//获取输出的声道个数
	int out_channel_nb;

	av_register_all();
	avformat_network_init();
	pFormatCtx = avformat_alloc_context();
	if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
		printf("Could not initialize SDL - %s\n", SDL_GetError());
	}

	char *filepath;
	int type;
	filepath = "test.mp3";
	type = AVMEDIA_TYPE_AUDIO;
	//打开输入文件
	if (avformat_open_input(&pFormatCtx, filepath, NULL, NULL) != 0){
		printf("Couldn't open input stream.\n");
		return -1;
	}
	//获取文件信息
	if (avformat_find_stream_info(pFormatCtx, NULL)<0){
		printf("Couldn't find stream information.\n");
		return -1;
	}
	//找到对应的type所在的pFormatCtx->streams的索引位置
	index = -1;
	for (int i = 0; inb_streams; i++)
		if (pFormatCtx->streams[i]->codec->codec_type == type){
			index = i;
			break;
		}
	if (index == -1){
		printf("Didn't find a video stream.\n");
		return -1;
	}
	//获取解码器
	pCodeCtx = pFormatCtx->streams[index]->codec;
	pCodec = avcodec_find_decoder(pCodeCtx->codec_id);
	if (pCodec == NULL){
		printf("Codec not found.\n");
		return -1;
	}
	//打开解码器
	if (avcodec_open2(pCodeCtx, pCodec, NULL)<0){
		printf("Could not open codec.\n");
		return -1;
	}

	//重采样设置选项-----------------------------------------------------------start
	//输入的采样格式
	in_sample_fmt = pCodeCtx->sample_fmt;
	//输出的采样格式 16bit PCM
	out_sample_fmt = AV_SAMPLE_FMT_S16;
	//输入的采样率
	in_sample_rate = pCodeCtx->sample_rate;
	//输出的采样率
	out_sample_rate = 44100;
	//输入的声道布局
	in_ch_layout = pCodeCtx->channel_layout;
	if (in_ch_layout <= 0)
	{
		in_ch_layout = av_get_default_channel_layout(pCodeCtx->channels);
	}
	//输出的声道布局
	out_ch_layout = AV_CH_LAYOUT_MONO;

	//frame->16bit 44100 PCM 统一音频采样格式与采样率
	swrCtx = swr_alloc();
	swr_alloc_set_opts(swrCtx, out_ch_layout, out_sample_fmt, out_sample_rate, in_ch_layout, in_sample_fmt,
		in_sample_rate, 0, NULL);
	swr_init(swrCtx);
	//重采样设置选项-----------------------------------------------------------end

	//获取输出的声道个数
	out_channel_nb = av_get_channel_layout_nb_channels(out_ch_layout);
	//SDL_AudioSpec
	wanted_spec.freq = out_sample_rate;
	wanted_spec.format = AUDIO_S16SYS;
	wanted_spec.channels = out_channel_nb;
	wanted_spec.silence = 0;
	wanted_spec.samples = pCodeCtx->frame_size;
	wanted_spec.callback = fill_audio;//回调函数
	wanted_spec.userdata = pCodeCtx;
	if (SDL_OpenAudio(&wanted_spec, NULL)<0){
		printf("can't open audio.\n");
		return -1;
	}

	//编码数据
	AVPacket *packet = (AVPacket *)av_malloc(sizeof(AVPacket));
	//解压缩数据
	AVFrame *frame = av_frame_alloc();
	//存储pcm数据
	uint8_t *out_buffer = (uint8_t *)av_malloc(2 * 44100);

	int ret, got_frame, framecount = 0;
	//一帧一帧读取压缩的音频数据AVPacket
	while (1)
		while (av_read_frame(pFormatCtx, packet) >= 0) {
			if (packet->stream_index == index) {
				//解码AVPacket->AVFrame
				ret = avcodec_decode_audio4(pCodeCtx, frame, &got_frame, packet);
				if (ret < 0) {
					printf("%s", "解码完成");
				}
				//非0，正在解码
				int out_buffer_size;
				if (got_frame) {
					printf("解码%d帧", framecount++);
					swr_convert(swrCtx, &out_buffer, 2 * 44100, (const uint8_t **)frame->data, frame->nb_samples);
					//获取sample的size
					out_buffer_size = av_samples_get_buffer_size(NULL, out_channel_nb, frame->nb_samples,
						out_sample_fmt, 1);
					//设置音频数据缓冲,PCM数据
					audio_chunk = (Uint8 *)out_buffer;
					//设置音频数据长度
					audio_len = out_buffer_size;
					audio_pos = audio_chunk;
					//回放音频数据 
					SDL_PauseAudio(0);
					while (audio_len>0)//等待直到音频数据播放完毕! 
						SDL_Delay(10);

					packet->data += ret;
					packet->size -= ret;
				}
			}
		}
	av_free(out_buffer);
	av_frame_free(&frame);
	av_free_packet(packet);
    SDL_CloseAudio();//关闭音频设备 
	swr_free(&swrCtx);
    SDL_Quit();
	avcodec_close(pCodeCtx);
	avformat_close_input(&pFormatCtx);
	return 0;
}