PCM文件转换为MP3文件

简要描述

主要协助云上越秀App将PCM音频文件转码成MP3文件功能代码示例；

主要内容

PCM录制示例代码：

引入第三方库：

pod 'mp3lame-for-ios'

代码片段:

- (void)startSpeechRecognizerWithFileName:(NSString *)fileName {
    [self.iFlySpeechRecognizer cancel];
    self.jsons = @[].mutableCopy;
    if ([PHAIUtils isNilOrEmpty:fileName]) {
        self.fileName = [PHAIFileManager generateFileName];
    } else {
        self.fileName = fileName;
    }
    NSString *pcmFileName = [NSString stringWithFormat:@"%@.pcm", self.fileName];
    //asr_audio_path 是录音文件名，设置value为nil或者为空取消保存，默认保存目录在Library/cache下。
    [_iFlySpeechRecognizer setParameter:pcmFileName forKey:[IFlySpeechConstant ASR_AUDIO_PATH]];
    //启动识别服务
    [self.iFlySpeechRecognizer startListening];
}
- (void)onCompleted:(IFlySpeechError *)error {
    IFlyLog(@"%s",__func__);
    self.result = nil;
    if (error.errorCode != 0) {
        IFlyLog(@"语音识别出现问题：%@", error.errorDesc);
    } else {
        PHAIFileManager *fileManager = PHAIFileManager.sharedManager;
        NSString *fileName = self.fileName;
        NSString *pcmFilePath = [fileManager getCachesPCMURLWithName:fileName].path;
        NSString *mp3FilePath = [fileManager getIATAudioFileWithName:fileName].path;
        int sampleRate = [PHAIIATConfig.sharedInstance.sampleRate intValue];
        __weak typeof(self) weakSelf = self;
        [PHAIMP3Encoder conventToMp3WithCafFilePath:pcmFilePath
                                        mp3FilePath:mp3FilePath
                                         sampleRate:sampleRate
                                           callback:^(BOOL complete) {
            if (weakSelf.delegate && [weakSelf.delegate respondsToSelector:@selector(mp3EnconderComplete:fileName:)]) {
                [weakSelf.delegate mp3EnconderComplete:complete fileName:fileName];
            }
            AudioEncoderLog(@"转码完成");
        }];
    }
    if (self.delegate && [self.delegate respondsToSelector:@selector(recongnizingComplete:)]) {
        [self.delegate recongnizingComplete:error.errorCode == 0];
    }
}

PCM转换成MP3的示例代码：

PHAIMP3Encoder.h

#import <Foundation/Foundation.h>
NS_ASSUME_NONNULL_BEGIN
@interface PHAIMP3Encoder : NSObject
+ (void)conventToMp3WithCafFilePath:(NSString *)cafFilePath
                        mp3FilePath:(NSString *)mp3FilePath
                           callback:(void(^)(BOOL complete))callback;
+ (void)conventToMp3WithCafFilePath:(NSString *)cafFilePath
                        mp3FilePath:(NSString *)mp3FilePath
                         sampleRate:(int)sampleRate
                           callback:(void(^)(BOOL complete))callback;
@end
NS_ASSUME_NONNULL_END

PHAIMP3Encoder.m

#import "PHAIMP3Encoder.h"
#import "lame/lame.h"
#import "PHAILogFunctions.h"
@implementation PHAIMP3Encoder
+ (void)conventToMp3WithCafFilePath:(NSString *)cafFilePath
                        mp3FilePath:(NSString *)mp3FilePath
                           callback:(void (^)(BOOL))callback {
    [self conventToMp3WithCafFilePath:cafFilePath
                          mp3FilePath:mp3FilePath
                           sampleRate:16000
                             callback:^(BOOL complete) {
        callback(complete);
    }];
}
+ (void)conventToMp3WithCafFilePath:(NSString *)cafFilePath
                        mp3FilePath:(NSString *)mp3FilePath
                         sampleRate:(int)sampleRate
                           callback:(void(^)(BOOL complete))callback {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        @try {
            int read, write;
            FILE *pcm = fopen([cafFilePath cStringUsingEncoding:1], "rb");  //source 被转换的音频文件位置
            if (pcm == NULL) {
                if ([NSFileManager.defaultManager fileExistsAtPath:cafFilePath]) {
                    pcm = fopen([cafFilePath cStringUsingEncoding:1], "rb");
                } else {
                    AudioEncoderLog(@"文件无法打开: %@ %d", cafFilePath, [NSFileManager.defaultManager fileExistsAtPath:cafFilePath]);
                    callback(NO);
                    return;
                }
            }
            fseek(pcm, 4*1024, SEEK_CUR);                                   //skip file header
            FILE *mp3 = fopen([mp3FilePath cStringUsingEncoding:1], "wb+");  //output 输出生成的Mp3文件位置
            const int PCM_SIZE = sampleRate / 20 + 7200;
            const int MP3_SIZE = PCM_SIZE;
            short int pcm_buffer[PCM_SIZE*2];
            unsigned char mp3_buffer[MP3_SIZE];
            lame_t lame = lame_init();
            lame_set_in_samplerate(lame, sampleRate);
            lame_set_num_channels(lame,1);//设置1为单通道，默认为2双通道
            lame_set_VBR(lame, vbr_default);
            lame_init_params(lame);
            do {
                read = (int)fread(pcm_buffer, sizeof(short int), PCM_SIZE, pcm);
                if (read == 0) {
                    write = lame_encode_flush(lame, mp3_buffer, MP3_SIZE);
                } else {
                    write = lame_encode_buffer(lame, pcm_buffer, NULL, read, mp3_buffer, MP3_SIZE);
                }
                fwrite(mp3_buffer, sizeof(char), write, mp3);
            } while (read != 0);
            lame_mp3_tags_fid(lame, mp3);
            lame_close(lame);
            fclose(mp3);
            fclose(pcm);
        } @catch (NSException *exception) {
            AudioEncoderLog(@"%@",[exception description]);
            if (callback) {
                callback(NO);
            }
        }
        @finally {
            AudioEncoderLog(@"-----\n  MP3生成成功: %@   -----  \n", mp3FilePath);
            if (callback) {
                callback(YES);
            }
        }
    });
}
@end