我正在尝试构建一个应用程序，该应用程序将使用 AVFoundation 类更改视频的组成，但希望能够先播放视频。我已经编写了一些代码来做到这一点，但是当我播放视频时声音不起作用。
我尝试使用 Apple 示例代码来执行此操作。
下面是我的代码：
-(void)loadAssets
{
NSArray *requestedKeys = [NSArray arrayWithObjects:kTracksKey, kPlayableKey, nil];
/* Tells the asset to load the values of any of the specified keys that are not already loaded. */
[asset loadValuesAsynchronouslyForKeys:requestedKeys completionHandler:
^{
dispatch_async( dispatch_get_main_queue(),
^{
/* IMPORTANT: Must dispatch to main queue in order to operate on the AVPlayer and AVPlayerItem. */
[self prepareToPlayAsset:asset withKeys:requestedKeys];
});
}];
}
- (void)prepareToPlayAsset:(AVURLAsset *)assetURL withKeys:(NSArray *)requestedKeys
{
/* Make sure that the value of each key has loaded successfully. */
for (NSString *thisKey in requestedKeys)
{
NSError *error = nil;
AVKeyValueStatus keyStatus = [assetURL statusOfValueForKey:thisKey error:&error];
if (keyStatus == AVKeyValueStatusFailed)
{
[self assetFailedToPrepareForPlayback:error];
return;
}
}
/* Use the AVAsset playable property to detect whether the asset can be played. */
if (!assetURL.playable)
{
/* Generate an error describing the failure. */
NSString *localizedDescription = NSLocalizedString(@"Item cannot be played", @"Item cannot be played description");
NSString *localizedFailureReason = NSLocalizedString(@"The assets tracks were loaded, but could not be made playable.", @"Item cannot be played failure reason");
NSDictionary *errorDict = [NSDictionary dictionaryWithObjectsAndKeys:
localizedDescription, NSLocalizedDescriptionKey,
localizedFailureReason, NSLocalizedFailureReasonErrorKey,
nil];
NSError *assetCannotBePlayedError = [NSError errorWithDomain:@"StitchedStreamPlayer" code:0 userInfo:errorDict];
/* Display the error to the user. */
[self assetFailedToPrepareForPlayback:assetCannotBePlayedError];
return;
}
/* At this point we're ready to set up for playback of the asset. */
/* Stop observing our prior AVPlayerItem, if we have one. */
if (self.playerItem)
{
/* Remove existing player item key value observers and notifications. */
[self.playerItem removeObserver:self forKeyPath:kStatusKey];
[[NSNotificationCenter defaultCenter] removeObserver:self
name:AVPlayerItemDidPlayToEndTimeNotification
object:self.playerItem];
}
/* Create a new instance of AVPlayerItem from the now successfully loaded AVAsset. */
self.playerItem = [AVPlayerItem playerItemWithAsset:asset];
/* Observe the player item "status" key to determine when it is ready to play. */
[self.playerItem addObserver:self
forKeyPath:kStatusKey
options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
context:VideoPlaybackViewControllerStatusObservationContext];
/* When the player item has played to its end time we'll toggle
the movie controller Pause button to be the Play button */
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(playerItemDidReachEnd:)
name:AVPlayerItemDidPlayToEndTimeNotification
object:self.playerItem];
seekToZeroBeforePlay = NO;
/* Create new player, if we don't already have one. */
if (![self player])
{
/* Get a new AVPlayer initialized to play the specified player item. */
self.player=[AVPlayer playerWithPlayerItem:self.playerItem];
[self.playerView setPlayer:self.player];
// Observe the AVPlayer "currentItem" property to find out when any
//AVPlayer replaceCurrentItemWithPlayerItem: replacement will/did
//occur.
[self.player addObserver:self
forKeyPath:kCurrentItemKey
options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
context:VideoPlaybackViewControllerCurrentItemObservationContext];
}
// Make our new AVPlayerItem the AVPlayer's current item.
if (self.player.currentItem != self.playerItem)
{
// Replace the player item with a new player item. The item replacement occurs
//asynchronously; observe the currentItem property to find out when the
//replacement will/did occur
[[self player] replaceCurrentItemWithPlayerItem:self.playerItem];
[self syncUI];
}
}
- (void)observeValueForKeyPath:(NSString*) path
ofObject:(id)object
change:(NSDictionary*)change
context:(void*)context
{
/* AVPlayerItem "status" property value observer. */
if (context == VideoPlaybackViewControllerStatusObservationContext)
{
[self syncUI];
AVPlayerStatus status = [[change objectForKey:NSKeyValueChangeNewKey] integerValue];
switch (status)
{
/* Indicates that the status of the player is not yet known because
it has not tried to load new media resources for playback */
case AVPlayerStatusUnknown:
{
[self disablePlayerButtons];
}
break;
case AVPlayerStatusReadyToPlay:
{
/* Once the AVPlayerItem becomes ready to play, i.e.
[playerItem status] == AVPlayerItemStatusReadyToPlay,
its duration can be fetched from the item. */
//[self initScrubberTimer];
//[self enableScrubber];
[self enablePlayerButtons];
}
break;
case AVPlayerStatusFailed:
{
AVPlayerItem *playerItem = (AVPlayerItem *)object;
[self assetFailedToPrepareForPlayback:playerItem.error];
}
break;
}
}
/* AVPlayer "currentItem" property observer.
Called when the AVPlayer replaceCurrentItemWithPlayerItem:
replacement will/did occur. */
else if (context == VideoPlaybackViewControllerCurrentItemObservationContext)
{
AVPlayerItem *newPlayerItem = [change objectForKey:NSKeyValueChangeNewKey];
/* Is the new player item null? */
if (newPlayerItem == (id)[NSNull null])
{
[self disablePlayerButtons];
//[self disableScrubber];
}
else /* Replacement of player currentItem has occurred */
{
/* Set the AVPlayer for which the player layer displays visual output. */
[self.playerView setPlayer:self.player];
//[self setViewDisplayName];
/* Specifies that the player should preserve the video’s aspect ratio and
fit the video within the layer’s bounds. */
//[mPlaybackView setVideoFillMode:AVLayerVideoGravityResizeAspect];
[self syncUI];
}
}
else
{
[super observeValueForKeyPath:path ofObject:object change:change context:context];
}
}
有什么帮助吗？