Separate Audio from Video - ios

Question

float sliderValue = 0.5;
NSURL *audio_url = [[NSBundle mainBundle] pathForResource:#“video_fileName” ofType:#"mp4"]];
AVURLAsset* audio_Asset = [[AVURLAsset alloc]initWithURL:audio_url options:nil];
AVMutableAudioMixInputParameters *audioInputParams = [AVMutableAudioMixInputParameters audioMixInputParameters];
NSString* formattedNumber = [NSString stringWithFormat:#"%.01f", sliderValue];
NSLog(#"formattedNumber %#",formattedNumber);
NSLog(#"formattedNumber %.01f",[formattedNumber floatValue]);
[audioInputParams setVolume:[formattedNumber floatValue] atTime:kCMTimeZero];
[audioInputParams setTrackID:[[[audio_Asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] trackID]];
AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix];
audioMix.inputParameters = [NSArray arrayWithObject:audioInputParams];
AVAssetExportSession *exportSession=[AVAssetExportSession exportSessionWithAsset:audio_Asset presetName:AVAssetExportPresetAppleM4A];
exportSession.audioMix = audioMix;
exportSession.outputURL=[NSURL fileURLWithPath:audioPath];
exportSession.outputFileType=AVFileTypeAppleM4A;
[exportSession exportAsynchronouslyWithCompletionHandler:^{
if (exportSession.status==AVAssetExportSessionStatusFailed) {
NSLog(#"failed");
}
else {
NSLog(#"AudioLocation : %#",audioPath);
}
}];
Issue: get asset blank, so app crashes.
[[audio_Asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]
[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array';

Answer 1

The crash has described the issue, you are trying to access an array beyond it's bounds. change:
[audioInputParams setTrackID:[[[audio_Asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] trackID]];
to:
NSArray * tracks = [audio_Asset tracksWithMediaType:AVMediaTypeAudio];
if([tracks count]) {
[audioInputParams setTrackID:[[tracks firstObject] trackID]];
}
Your main issue may be that loading an AVURLAsset might not immediately load all the tracks. You can wrap your method (after getting audio_Asset) in the load method to have better guarantee:
NSString *tracksKey = #"tracks";
[audio_Asset loadValuesAsynchronouslyForKeys:#[tracksKey] completionHandler: ^{
// rest of the code here