AVMutableCompositionTrack - insertTimeRange - insertEmptyTimeRange issue

Question

I have a strange problem: I want to generate a new sound file out of two soundfiles and silence.

sound1: 2 seconds long + silence: 2 seconds silence + sound2: 2 seconds long

When I try the code below, I get a 6 seconds long soundfile with all the parts, but in a different order! The order is: sound1, sound2, silence

I am not able to put this silence in the middle of this composition (also not at the beginning). Is this a typical behavior or do I something wrong?

Here is the code for putting the segments together:

[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [audio1 duration])  ofTrack:clipAudioTrack1 atTime:kCMTimeZero error:nil];
[compositionAudioTrack insertEmptyTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMake(2, 1))];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [audio2 duration])  ofTrack:clipAudioTrack2 atTime:CMTimeMake(4, 1) error:nil];

Perhaps someone has an idea? Thank you in advance!

By the way: following code without the insertEmptyTimeRange-line doesn't work either, it just generates 4 seconds of sound and sound2 slides to the end of sound1:

    [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [audio1 duration])  ofTrack:clipAudioTrack1 atTime:kCMTimeZero error:nil];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [audio2 duration])  ofTrack:clipAudioTrack2 atTime:CMTimeMake(4, 1) error:nil];

It seems that it is not allowed that there is "nothing" between segments!?

Answer 1

Still don't know what this "insertEmptyTimeRange" means. I made a work around with a "silence"-audio file which has nothing in it. I put this empty audio file between the two sound files and this does it for me. Question closed ;) (But if someone could explain this "insertEmptyTimeRange" this would be still interesting...)

Answer 2

I got it working as follows:

[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMake(2,1))
                               ofTrack:audioTrack
                                atTime:kCMTimeZero
                                error:nil];
[compositionAudioTrack insertEmptyTimeRange:CMTimeRangeMake(CMTimeMake(2, 1), CMTimeMake(4, 1))];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMake(2,1))  
                               ofTrack:audioTrack 
                                atTime:CMTimeMake(4, 1)
                                 error:nil];

The "empty time range" needs to be (2,4) if your sounds are from (0,2) and (4,6).

Answer 3

Not sure if its late,

insertEmptyTimeRange : If you insert an empty time range into the track, any media that was presented during that interval prior to the insertion will be presented instead immediately afterward.

So all you have to do is add both the clips first and then add the emptytime range at time 2. This should work

insertTimeRange(0 to 2)
insertTimeRange(2 to 4)
insertEmptyTimeRange(2 to 4)