/*

     File: AVSETrimCommand.m

 Abstract: A subclass of AVSECommand which uses AVMutableComposition to trim a movie. This tool trims a movie to half its original length.

  Version: 1.1

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#import "AVSETrimCommand.h"

@implementation AVSETrimCommand

- (void)performWithAsset:(AVAsset*)asset

{

    AVAssetTrack *assetVideoTrack = nil;

    AVAssetTrack *assetAudioTrack = nil;

    // Check if the asset contains video and audio tracks

    if ([[asset tracksWithMediaType:AVMediaTypeVideo] count] != 0) {

        assetVideoTrack = [asset tracksWithMediaType:AVMediaTypeVideo][0];

    }

    if ([[asset tracksWithMediaType:AVMediaTypeAudio] count] != 0) {

        assetAudioTrack = [asset tracksWithMediaType:AVMediaTypeAudio][0];

    }

    CMTime insertionPoint = kCMTimeZero;

    NSError *error = nil;

    // Trim to half duration

    double halfDuration = CMTimeGetSeconds([asset duration])/2.0;

    CMTime trimmedDuration = CMTimeMakeWithSeconds(halfDuration, 1);

    // Step 1

    //  Create a composition with the given asset and insert audio and video tracks for half the duration into it from the asset

    if(!self.mutableComposition) {

        // Check if a composition already exists, i.e., another tool has been applied

        // Create a new composition

        self.mutableComposition = [AVMutableComposition composition];

        // Insert half time range of the video and audio tracks from AVAsset

        if(assetVideoTrack != nil) {

            AVMutableCompositionTrack *compositionVideoTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

            [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, trimmedDuration) ofTrack:assetVideoTrack atTime:insertionPoint error:&error];

        }

        if(assetAudioTrack != nil) {

            AVMutableCompositionTrack *compositionAudioTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

            [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, trimmedDuration) ofTrack:assetAudioTrack atTime:insertionPoint error:&error];

        }

    }else {

        // Remove the second half of the existing composition to trim

        [self.mutableComposition removeTimeRange:CMTimeRangeMake(trimmedDuration, [self.mutableComposition duration])];

    }

    // Step 2

    // Notify AVSEViewController about trim operation completion

    [[NSNotificationCenter defaultCenter] postNotificationName:AVSEEditCommandCompletionNotification object:self];

}

@end