Black frames in AVMutableComposition

This question is quite related to AVMutableComposition - Blank/Black frame between videos assets but as I am not using an AVAssetExportSession the answers doesn't fit my problem.

I'm using an AVMutableComposition to create a video composition and I'm reading it using an AVAssetReader (I need to have the frame data, I can't use a AVPlayer) but I often have black frames between my video chunks (there is no glitch noticeable in the audio).

I create my Composition as

AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

NSMutableArray* durationList = [NSMutableArray array];
NSMutableArray* videoList= [NSMutableArray array];
NSMutableArray* audioList= [NSMutableArray array];

for (NSInteger i = 0; i < [clips count]; i++)
{
    AVURLAsset *myasset = [clips objectAtIndex:i];
    AVAssetTrack *clipVideoTrack = [[myasset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    [videoList addObject:clipVideoTrack];

    AVAssetTrack *clipAudioTrack = [[myasset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
    [audioList addObject:clipAudioTrack];

    CMTime clipDuration = [myasset duration];
    CMTimeRange clipRange = CMTimeRangeMake(kCMTimeZero, clipDuration);
    [durationList addObject:[NSValue valueWithCMTimeRange:clipRange]];
}

[compositionVideoTrack insertTimeRanges:durationList ofTracks:videoList atTime:kCMTimeZero error:nil];
[compositionAudioTrack insertTimeRanges:durationList ofTracks:audioList atTime:kCMTimeZero error:nil];

I also tried to insert each track manually in my composition but I have the same phenomenon.