speech_lib/ios/Classes/M4aToPcmHelper.m

//
//  M4aToPcmHelper.m
//  TianyiProSwift
//
//  Created by i2国际私塾 on 2017/3/21.
//  Copyright © 2017年 Chengdu Aitu Education Technology Ltd. All rights reserved.
//

#import "M4aToPcmHelper.h"
#import <AudioToolbox/AudioToolbox.h>
#import <AVFoundation/AVFoundation.h>
#import <MediaPlayer/MediaPlayer.h>

@implementation M4aToPcmHelper

/**
 *  根据m4a音频转化成pcm格式的音频
 *
 *  @param urlStr 音频路径
 *
 *  @return pcm格式的[Int16]的Data
 */

+ (NSURL *) M4aToPcmWithUrl:(NSURL *)url {
    NSArray *dirs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectoryPath = [dirs objectAtIndex:0];
    NSString *exportPath = [documentsDirectoryPath stringByAppendingPathComponent:@"pcmData.pcm"];
    if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) {
        [[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];
    }
    NSURL *exportURL = [NSURL fileURLWithPath:exportPath];
    
    AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:url options:nil];
    NSError *assetError = nil;
    AVAssetReader *assetReader = [AVAssetReader assetReaderWithAsset:songAsset
                                                               error:&assetError];
    if (assetError) {
        NSLog (@"error: %@", assetError);
        return nil;
    }
    
    AVAssetWriter *assetWriter = [AVAssetWriter assetWriterWithURL:exportURL
                                                          fileType:AVFileTypeCoreAudioFormat
                                                             error:&assetError];
    
    AVAssetReaderOutput *assetReaderOutput = [AVAssetReaderAudioMixOutput
                                              assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks
                                              audioSettings: nil];
    
    [assetReader addOutput: assetReaderOutput];
    
    if (assetError) {
        NSLog (@"error: %@", assetError);
        return nil;
    }
    AudioChannelLayout channelLayout;
    memset(&channelLayout, 0, sizeof(AudioChannelLayout));
    channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
    NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                    [NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,
                                    [NSNumber numberWithFloat:8000.0], AVSampleRateKey,
                                    [NSNumber numberWithInt:2], AVNumberOfChannelsKey,
                                    [NSData dataWithBytes:&channelLayout length:sizeof(AudioChannelLayout)], AVChannelLayoutKey,
                                    [NSNumber numberWithInt:16], AVLinearPCMBitDepthKey,
                                    [NSNumber numberWithBool:NO], AVLinearPCMIsNonInterleaved,
                                    [NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,
                                    [NSNumber numberWithBool:NO], AVLinearPCMIsBigEndianKey,
                                    nil];
    AVAssetWriterInput *assetWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio
                                                                              outputSettings:outputSettings];
    if ([assetWriter canAddInput:assetWriterInput]) {
        [assetWriter addInput:assetWriterInput];
    } else {
        NSLog (@"can't add asset writer input... die!");
        return nil;
    }
    
    assetWriterInput.expectsMediaDataInRealTime = YES;
    
    [assetWriter startWriting];
    [assetReader startReading];
    
    AVAssetTrack *soundTrack = [songAsset.tracks objectAtIndex:0];
    CMTime startTime = CMTimeMake (0, soundTrack.naturalTimeScale);
    [assetWriter startSessionAtSourceTime: kCMTimeZero];
    
//    while (assetWriterInput.readyForMoreMediaData == FALSE) {
//        NSDate *maxDate = [NSDate dateWithTimeIntervalSinceNow:0.1];
//        [[NSRunLoop currentRunLoop] runUntilDate:maxDate];
//        NSLog(@"等待几秒试试");
//    }
//    __block UInt64 convertedByteCount = 0;
//    BOOL isFinish = false;
    
    CMSampleBufferRef sample = [assetReaderOutput copyNextSampleBuffer];
    while(sample != NULL)
    {
      while (TRUE) {
        if ([assetWriterInput isReadyForMoreMediaData]) {
          [assetWriterInput appendSampleBuffer:sample];
          break;
        }
      }
      CFRelease( sample );
      sample = [assetReaderOutput copyNextSampleBuffer];
    }
    
//    while (assetWriterInput.readyForMoreMediaData) {
//        NSLog(@"ready for");
//        CMSampleBufferRef nextBuffer = [assetReaderOutput copyNextSampleBuffer];
//        if (nextBuffer) {
//            // append buffer
//            [assetWriterInput appendSampleBuffer: nextBuffer];
//            convertedByteCount += CMSampleBufferGetTotalSampleSize (nextBuffer);
//
//        }
//        else{
//            // done!
//            [assetWriterInput markAsFinished];
//            [assetWriter finishWritingWithCompletionHandler:^{
//            }];
//            [assetReader cancelReading];
//            isFinish = true;
//
//            return exportURL;
//        }
//    }
        [assetWriterInput markAsFinished];
        [assetWriter finishWritingWithCompletionHandler:^{
        }];
        [assetReader cancelReading];
    return exportURL;
}

@end