Created
March 3, 2016 21:49
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Smooth AVPlayer scrolling performance fix
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| > DESCRIPTION OF PROBLEM | |
| > In Photos.app, Videos.app, and iMovie.app, local videos can be rewound using the video scrubber. Scrubbing backwards in a video is extremely smooth and satisfying. | |
| > | |
| > Using AVPlayer in our app, ScoreBreak, we cannot achieve the same smoothness when scrubbing a video backwards. There are reports on stack overflow which indicate that this is due to the codec used by AVPlayer. | |
| > | |
| > We would like to deliver the same beautiful user interaction with videos as offered by your system apps. Can you instruct us on how to achieve this while using AVFoundation? | |
| > | |
| > STEPS TO REPRODUCE | |
| > • Create test application which utilizes AVPlayer for local video file playback | |
| > • Scrub backwards using AVPlayer controller | |
| > • Compare against Photos.app (or iMovie) scrubbing performance | |
| > • Note that the scrolling is "jumpy", or choppy; not smooth | |
| I assume you are using the AVPlayer seekToTime method to perform seeks when scrubbing? | |
| And are you calling AVPlayer seekToTime in rapid succession when the user drags the scrubber? | |
| If you are calling AVPlayer seekToTime in rapid succession, this can have the effect of cancelling any seeks already in progress, resulting in a lot of seeking and not a lot of displaying of the target frames. Instead, you can use the completionHandler variety of that method ( | |
| seekToTime:completionHandler:) and wait for a seek in progress to complete first before issuing another. | |
| Here's an example: | |
| ``` | |
| - (void)_actuallySeekToTime | |
| { | |
| _isSeekInProgress = YES; | |
| CMTime seekTimeInProgress = _chaseTime; | |
| [_player seekToTime:seekTimeInProgress toleranceBefore:kCMTimeZero toleranceAfter:kCMTimeZero completionHandler: | |
| ^(BOOL isFinished) | |
| { | |
| if (CMTIME_COMPARE_INLINE(seekTimeInProgress, ==, _chaseTime)) | |
| _isSeekInProgress = NO; | |
| else | |
| [self _trySeekToChaseTime]; | |
| }]; | |
| } | |
| - (void)_trySeekToChaseTime | |
| { | |
| if (_playerCurrentItemStatus == AVPlayerItemStatusUnknown) | |
| { | |
| // do it when item becomes ready (KVO _player.currentItem.status) | |
| } | |
| else if (_playerCurrentItemStatus == AVPlayerItemStatusReadyToPlay) | |
| { | |
| [self _actuallySeekToTime]; | |
| } | |
| } | |
| - (void)stopPlayingAndSeekSmoothlyToTime:(CMTime)newChaseTime | |
| { | |
| [_player setRate:0.0]; | |
| if (CMTIME_COMPARE_INLINE(newChaseTime, !=, _chaseTime)) | |
| { | |
| _chaseTime = newChaseTime; | |
| if (!_isSeekInProgress) | |
| [self _trySeekToChaseTime]; | |
| } | |
| } | |
| ``` |
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