SBC介紹

1.SBC一般bai的音頻格式，藍牙傳輸在不支持AAC，aptx的時候都用SBC傳輸，音質一般，現(xiàn)在80%都是這種格式

代碼部分（用FFmpeg）

1.頭文件

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface SBCStreamDecoder : NSObject

@property (nonatomic,copy) void(^onRecvPCMData)(NSData *pcmData);


+(id)sharedInstance;


-(void)initSBCDecodec;
-(void)decodeSBCData:(NSData*)data;
/* 釋放SBC解碼器 */
- (void)finishSBCDecode;


@end

1.m文件

#import "SBCStreamDecoder.h"


#import <VideoToolbox/VideoToolbox.h>


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

#include <libavutil/frame.h>
#include <libavutil/mem.h>

#include <libavcodec/avcodec.h>





@interface SBCStreamDecoder (){
    AVCodecContext *codecContext;
    AVCodecParserContext *parserContext;
    AVFrame *decodecAVFrame;
    AVPacket *decodecAVPacket;
}
@property (assign, nonatomic) AVFrame *sbcFrame;
@property (assign, nonatomic) AVCodec *sbcCodec;
@property (assign, nonatomic) AVCodecContext *sbcCodecCtx;
@property (assign, nonatomic) AVPacket  *sbcPacket;
@property (assign, nonatomic)AVCodecParserContext *sbcParser;
@end
@implementation SBCStreamDecoder

static SBCStreamDecoder *sbcStreamDecoder = nil;
static dispatch_once_t onceToken;
+(id)sharedInstance
{
    dispatch_once(&onceToken, ^{
        sbcStreamDecoder = [[self alloc] init];
    });
    return sbcStreamDecoder;
}

//獲取format
-(int)get_format_from_sample_fmt:(const char **)fmt sampleFormat:(enum AVSampleFormat)sample_fmt{
    int i;
    struct sample_fmt_entry {
        enum AVSampleFormat sample_fmt; const char *fmt_be, *fmt_le;
    } sample_fmt_entries[] = {
        { AV_SAMPLE_FMT_U8P,  "u8p",    "u8p"    },
        { AV_SAMPLE_FMT_S16P,  "s16p",    "s16p"    },
        { AV_SAMPLE_FMT_S32P,  "s32p",    "s32p"    },
        { AV_SAMPLE_FMT_FLTP,  "fltp",    "fltp"    },
        { AV_SAMPLE_FMT_DBLP,  "u8",    "u8"    },
        { AV_SAMPLE_FMT_S64,  "s64",    "s64"    },
        { AV_SAMPLE_FMT_S64P,  "dblp",    "dblp"    },
        { AV_SAMPLE_FMT_NB,  "nb",    "nb"    },
        { AV_SAMPLE_FMT_U8,  "u8",    "u8"    },
        { AV_SAMPLE_FMT_S16, "s16be", "s16le" },
        { AV_SAMPLE_FMT_S32, "s32be", "s32le" },
        { AV_SAMPLE_FMT_FLT, "f32be", "f32le" },
        { AV_SAMPLE_FMT_DBL, "f64be", "f64le" },
    };
    *fmt = NULL;
    for (i = 0; i < FF_ARRAY_ELEMS(sample_fmt_entries); i++) {
        struct sample_fmt_entry *entry = &sample_fmt_entries[i];
        if (sample_fmt == entry->sample_fmt) {
            *fmt = AV_NE(entry->fmt_be, entry->fmt_le);
            NSLog(@"sample format %s \n",
                  av_get_sample_fmt_name(sample_fmt));
            return 0;
        }
    }
    NSLog(@"sample format %s is not supported as output format\n",
          av_get_sample_fmt_name(sample_fmt));
    return -1;
}


-(NSData*)decodeAudioData:(AVCodecContext *)dec_ctx pkt:(AVPacket *)pkt frame:(AVFrame*)frame {
    
    NSMutableData  *resultData = [[NSMutableData alloc]init];
    
    int i, ch;
    int ret, data_size;
    
    /* send the packet with the compressed data to the decoder */
    ret = avcodec_send_packet(dec_ctx, pkt);
    if (ret < 0) {
        NSLog(@"Error submitting the packet to the decoder\n");
        
    }
    
    /* read all the output frames (in general there may be any number of them */
    while (ret >= 0) {
        ret = avcodec_receive_frame(dec_ctx, frame);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF){
            NSLog (@"AVERROR \n");
            return  resultData;
        }else if (ret < 0) {
            NSLog (@"Error during decoding\n");
            return  resultData;
        }
        data_size = av_get_bytes_per_sample(dec_ctx->sample_fmt);
        NSLog(@"采樣位數(shù) %d", data_size);
        
        if (data_size < 0) {
            /* This should not occur, checking just for paranoia */
            NSLog (@"Failed to calculate data size\n");
            return  resultData;
        }
        NSLog(@"frame->nb_samples %d", frame->nb_samples);
        for (i = 0; i < frame->nb_samples; i++){
            for (ch = 0; ch < dec_ctx->channels; ch++){
                /*寫入到輸出文件中*/
                uint8_t *copyByte = malloc(data_size);
                memcpy(copyByte, frame->data[ch] + data_size*i, data_size);
                [resultData appendData: [NSData dataWithBytes:copyByte length:data_size]];
                free(copyByte);
            }
        }
        //               fwrite(frame->data[ch] + data_size*i, 1, data_size,outputFile);
    }
    NSLog (@"decode finish\n");
    
    return resultData;
}


-(void)initSBCDecodec{
    const AVCodec *codec;
    
    
    //初始化av_packet 結構體
    decodecAVPacket = av_packet_alloc();
    
    /* 查找支持解碼器 */
    codec = avcodec_find_decoder(AV_CODEC_ID_SBC);
    if (!codec) {
        NSLog(@"Codec not found\n");
        return;
        
    }
    /* 初始化解析器 */
    parserContext = av_parser_init(codec->id);
    if (!parserContext) {
        NSLog(@"Parser not found\n");
        return;
    }
    /* 初始化內容結構體 */
    codecContext = avcodec_alloc_context3(codec);
    if (!codecContext) {
        NSLog(@"Could not allocate audio codec context\n");
        return;
    }
    
    /* 打開解碼器 */
    if (avcodec_open2(codecContext, codec, NULL) < 0) {
        NSLog(@"Could not open codec\n");
        return;
    }
    
}

-(void)decodeSBCData:(NSData*)data{
    int  ret;
    if (!decodecAVFrame) {
        if (!(decodecAVFrame = av_frame_alloc())) {
            NSLog(@"Could not allocate audio frame\n");
            return;
        }
    }
    int  length = (int)data.length;
    while (length>0) {
        /* 開始解析文件 */
        uint8_t *decodData = (Byte*)[data bytes];
        ret = av_parser_parse2(parserContext, codecContext, &decodecAVPacket->data, &decodecAVPacket->size,
                               decodData, length,
                               AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
        if (ret < 0) {
            NSLog(@"Error while parsing\n");
            return;
        }
        /* 解析成功 開始解碼 */
        if (decodecAVPacket->size){
            NSData *pcmData = [self decodeAudioData:codecContext pkt:decodecAVPacket frame:decodecAVFrame];
            if(pcmData.length!=0){
           
                if(self.onRecvPCMData){
                    self.onRecvPCMData(pcmData);
                    
                }
            }
        }
        data = [data subdataWithRange:NSMakeRange(ret, length-ret)];
        length -= ret;
    }
    /* 解碼完成釋放解碼器 */
    decodecAVPacket->data = NULL;
    decodecAVPacket->size = 0;
    
}

-(void)finishSBCDecode{
    avcodec_free_context(&codecContext);
    av_parser_close(parserContext);
    av_frame_free(&decodecAVFrame);
    av_packet_free(&decodecAVPacket);
}




@end