Smooth video looping in iOS

问题:

Can anyone suggest a method by which you can achieve a completely smooth and seamless looping of a video clip in iOS? I have tried two methods, both of which produce a small pause when the video loops

1) AVPlayerLayer with the playerItemDidReachEnd notification setting off seekToTime:kCMTimeZero

I prefer to use an AVPlayerLayer (for other reasons), but this method produces a noticeable pause of around a second between loops.

2) MPMoviePlayerController with setRepeatMode:MPMovieRepeatModeOne

This results in a smaller pause, but it is still not perfect.

I'm not sure where to go from here. Can anyone suggest a soultion?

回答1:

I can concur @SamBrodkin's findings.

[[NSNotificationCenter defaultCenter]
    addObserver: self
    selector: @selector(myMovieFinishedCallback:)
    name: MPMoviePlayerPlaybackStateDidChangeNotification
    object: m_player];

and

-(void) myMovieFinishedCallback: (NSNotification*) aNotification
{
    NSLog( @"myMovieFinishedCallback: %@", aNotification );
    MPMoviePlayerController *movieController = aNotification.object;
    NSLog( @"player.playbackState = %d", movieController.playbackState );
}

fixed the non-looping issue on iOS 5 for me too.

回答2:

I just got this working on my iPad 3 running iOS 5.1.1, base SDK iOS 5.1

When setting up the movie player, set the repeat mode to MPMovieRepeatModeNone then add the notification

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(moviePlayerDidFinish:)
                                                 name:MPMoviePlayerPlaybackDidFinishNotification
                                               object:self.moviePlayer];

Then set up your selector to filter when the movie finishes playing

- (void)moviePlayerDidFinish:(NSNotification *)note {
    if (note.object == self.moviePlayer) {
        NSInteger reason = [[note.userInfo objectForKey:MPMoviePlayerPlaybackDidFinishReasonUserInfoKey] integerValue];
        if (reason == MPMovieFinishReasonPlaybackEnded) {
            [self.moviePlayer play];
        }
    }
}

Apple made some large changes to how the MPMoviePlayerController handles loading movie files when they changed from iOS 4 to iOS 5, so I do not know if this method will work when they release iOS 6

回答3:

To see an example that shows seamless looping of a background video (from an animated GIF) and switching between a pair of foreground character animations (with alpha channel), have a look at seamless-video-looping-on-ios. I tried to use AVPlayer in the past and had to give up on AVPlayer related solutions as they did not work well enough. See this SO question also iphone-smooth-transition-from-one-video-to-another.

回答4:

I investigated the same problem as reported by the original poster (small pause in the loop that was breaking the seamlessness). By luck I had another video sample that didn't had this behavior and found the explanation/different only later:

The sound track.

I suspect a very slow sound initialisation (routing?).

Removing the sound track was the easiest solution for me (no sound needed) but I will have to dig further (audio mixing options and testing the solution that have been posted in this thread).

Eric

回答5:

To avoid the gap when the video is rewound, using multiple copies of the same asset in a composition worked well for me.

AVURLAsset *tAsset = [AVURLAsset assetWithURL:tURL];
CMTimeRange tEditRange = CMTimeRangeMake(CMTimeMake(0, 1), CMTimeMake(tAsset.duration.value, tAsset.duration.timescale));
AVMutableComposition *tComposition = [[[AVMutableComposition alloc] init] autorelease];
for (int i = 0; i < 100; i++) { // Insert some copies.
    [tComposition insertTimeRange:tEditRange ofAsset:tAsset atTime:tComposition.duration error:nil];
}
AVPlayerItem *tAVPlayerItem = [[AVPlayerItem alloc] initWithAsset:tComposition];
AVPlayer *tAVPlayer = [[AVPlayer alloc] initWithPlayerItem:tAVPlayerItem];