/*

     File: APLSimpleEditor.m

 Abstract:  Simple editor setups a AVMutableComposition using supplied clips and time ranges. It also setups AVVideoComposition to perform custom compositor rendering. 

  Version: 1.1

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#import "APLSimpleEditor.h"

#import "APLCustomVideoCompositor.h"

#import "APLCustomVideoCompositionInstruction.h"

#import <CoreMedia/CoreMedia.h>

@interface APLSimpleEditor ()

@property (nonatomic, readwrite, retain) AVMutableComposition *composition;

@property (nonatomic, readwrite, retain) AVMutableVideoComposition *videoComposition;

@end

@implementation APLSimpleEditor

- (id)init

{

    if ((self = [super init])) {

        // initialization

    }

    return self;

}

- (void)buildTransitionComposition:(AVMutableComposition *)composition andVideoComposition:(AVMutableVideoComposition *)videoComposition

{

    CMTime nextClipStartTime = kCMTimeZero;

    NSInteger i;

    NSUInteger clipsCount = [_clips count];

    // Make transitionDuration no greater than half the shortest clip duration.

    CMTime transitionDuration = self.transitionDuration;

    for (i = 0; i < clipsCount; i++ ) {

        NSValue *clipTimeRange = [_clipTimeRanges objectAtIndex:i];

        if (clipTimeRange) {

            CMTime halfClipDuration = [clipTimeRange CMTimeRangeValue].duration;

            halfClipDuration.timescale *= 2; // You can halve a rational by doubling its denominator.

            transitionDuration = CMTimeMinimum(transitionDuration, halfClipDuration);

        }

    }

    // Add two video tracks and two audio tracks.

    AVMutableCompositionTrack *compositionVideoTracks[2];

    AVMutableCompositionTrack *compositionAudioTracks[2];

    compositionVideoTracks[0] = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

    compositionVideoTracks[1] = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

    compositionAudioTracks[0] = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

    compositionAudioTracks[1] = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

    CMTimeRange *passThroughTimeRanges = alloca(sizeof(CMTimeRange) * clipsCount);

    CMTimeRange *transitionTimeRanges = alloca(sizeof(CMTimeRange) * clipsCount);

    // Place clips into alternating video & audio tracks in composition, overlapped by transitionDuration.

    for (i = 0; i < clipsCount; i++ ) {

        NSInteger alternatingIndex = i % 2; // alternating targets: 0, 1, 0, 1, ...

        AVURLAsset *asset = [_clips objectAtIndex:i];

        NSValue *clipTimeRange = [_clipTimeRanges objectAtIndex:i];

        CMTimeRange timeRangeInAsset;

        if (clipTimeRange)

            timeRangeInAsset = [clipTimeRange CMTimeRangeValue];

        else

            timeRangeInAsset = CMTimeRangeMake(kCMTimeZero, [asset duration]);

        AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

        [compositionVideoTracks[alternatingIndex] insertTimeRange:timeRangeInAsset ofTrack:clipVideoTrack atTime:nextClipStartTime error:nil];

        AVAssetTrack *clipAudioTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

        [compositionAudioTracks[alternatingIndex] insertTimeRange:timeRangeInAsset ofTrack:clipAudioTrack atTime:nextClipStartTime error:nil];

        // Remember the time range in which this clip should pass through.

        // Second clip begins with a transition.

        // First clip ends with a transition.

        // Exclude those transitions from the pass through time ranges.

        passThroughTimeRanges[i] = CMTimeRangeMake(nextClipStartTime, timeRangeInAsset.duration);

        if (i > 0) {

            passThroughTimeRanges[i].start = CMTimeAdd(passThroughTimeRanges[i].start, transitionDuration);

            passThroughTimeRanges[i].duration = CMTimeSubtract(passThroughTimeRanges[i].duration, transitionDuration);

        }

        if (i+1 < clipsCount) {

            passThroughTimeRanges[i].duration = CMTimeSubtract(passThroughTimeRanges[i].duration, transitionDuration);

        }

        // The end of this clip will overlap the start of the next by transitionDuration.

        // (Note: this arithmetic falls apart if timeRangeInAsset.duration < 2 * transitionDuration.)

        nextClipStartTime = CMTimeAdd(nextClipStartTime, timeRangeInAsset.duration);

        nextClipStartTime = CMTimeSubtract(nextClipStartTime, transitionDuration);

        // Remember the time range for the transition to the next item.

        if (i+1 < clipsCount) {

            transitionTimeRanges[i] = CMTimeRangeMake(nextClipStartTime, transitionDuration);

        }

    }

    // Set up the video composition if we are to perform crossfade transitions between clips.

    NSMutableArray *instructions = [NSMutableArray array];

    // Cycle between "pass through A", "transition from A to B", "pass through B"

    for (i = 0; i < clipsCount; i++ ) {

        NSInteger alternatingIndex = i % 2; // alternating targets

        if (videoComposition.customVideoCompositorClass) {

            APLCustomVideoCompositionInstruction *videoInstruction = [[APLCustomVideoCompositionInstruction alloc] initPassThroughTrackID:compositionVideoTracks[alternatingIndex].trackID forTimeRange:passThroughTimeRanges[i]];

            [instructions addObject:videoInstruction];

        }

        else {

            // Pass through clip i.

            AVMutableVideoCompositionInstruction *passThroughInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];

            passThroughInstruction.timeRange = passThroughTimeRanges[i];

            AVMutableVideoCompositionLayerInstruction *passThroughLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTracks[alternatingIndex]];

            passThroughInstruction.layerInstructions = [NSArray arrayWithObject:passThroughLayer];

            [instructions addObject:passThroughInstruction];

        }

        if (i+1 < clipsCount) {

            // Add transition from clip i to clip i+1.

            if (videoComposition.customVideoCompositorClass) {

                APLCustomVideoCompositionInstruction *videoInstruction = [[APLCustomVideoCompositionInstruction alloc] initTransitionWithSourceTrackIDs:@[[NSNumber numberWithInt:compositionVideoTracks[0].trackID], [NSNumber numberWithInt:compositionVideoTracks[1].trackID]] forTimeRange:transitionTimeRanges[i]];

                if (alternatingIndex == 0) {

                    // First track -> Foreground track while compositing

                    videoInstruction.foregroundTrackID = compositionVideoTracks[alternatingIndex].trackID;

                    // Second track -> Background track while compositing

                    videoInstruction.backgroundTrackID = compositionVideoTracks[1-alternatingIndex].trackID;

                }

                [instructions addObject:videoInstruction];

            }

            else {

                AVMutableVideoCompositionInstruction *transitionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];

                transitionInstruction.timeRange = transitionTimeRanges[i];

                AVMutableVideoCompositionLayerInstruction *fromLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTracks[alternatingIndex]];

                AVMutableVideoCompositionLayerInstruction *toLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTracks[1-alternatingIndex]];

                transitionInstruction.layerInstructions = [NSArray arrayWithObjects:fromLayer, toLayer, nil];

                [instructions addObject:transitionInstruction];

            }

        }       

    }

    videoComposition.instructions = instructions;

}

- (void)buildCompositionObjectsForPlayback

{

    if ( (_clips == nil) || [_clips count] == 0 ) {

        self.composition = nil;

        self.videoComposition = nil;

        return;

    }

    CGSize videoSize = [[_clips objectAtIndex:0] naturalSize];

    AVMutableComposition *composition = [AVMutableComposition composition];

    AVMutableVideoComposition *videoComposition = nil;

    composition.naturalSize = videoSize;

    // With transitions:

    // Place clips into alternating video & audio tracks in composition, overlapped by transitionDuration.

    // Set up the video composition to cycle between "pass through A", "transition from A to B",

    // "pass through B"

    videoComposition = [AVMutableVideoComposition videoComposition];

    if (self.transitionType == 0) { // Diagonal Wipe

        videoComposition.customVideoCompositorClass = [APLDiagonalWipeCompositor class];

    } else { // Cross Dissolve

        videoComposition.customVideoCompositorClass = [APLCrossDissolveCompositor class];

    }

    [self buildTransitionComposition:composition andVideoComposition:videoComposition];

    if (videoComposition) {

        // Every videoComposition needs these properties to be set:

        videoComposition.frameDuration = CMTimeMake(1, 30); // 30 fps

        videoComposition.renderSize = videoSize;

    }

    self.composition = composition;

    self.videoComposition = videoComposition;

}

- (AVPlayerItem *)getPlayerItem

{

    AVPlayerItem *playerItem = [AVPlayerItem playerItemWithAsset:self.composition];

    playerItem.videoComposition = self.videoComposition;

    return playerItem;

}

@end