Question

[编辑：我能够找到解决方法，见下文。]

我正在尝试从S3流式传输多个远程MP4剪辑，将它们按顺序播放为一个连续视频（以便在剪辑内和剪辑之间进行清理），不会出现口吃，而无需先将其明确下载到设备中。但是，我发现剪辑缓冲非常缓慢（即使在快速的网络连接上），并且无法找到解决该问题的适当方法。

我一直在尝试使用AVPlayer，因为AVPlayer与AVMutableComposition一起播放提供的视频曲目作为一个连续曲目（与AVQueuePlayer不同，我收集分别播放每个视频，因此不支持剪辑之间的连续擦洗。）

当我将其中一个资产直接粘贴到AVPlayerItem并播放（没有AVMutableComposition）时，它会快速缓冲。但是使用AVMutableComposition，视频会在第二个剪辑上开始非常糟糕（我的测试用例有6个剪辑，每个剪辑大约6秒），而音频一直在继续。在它播放一次后，如果我倒回到开头，它会非常流畅地播放，所以我认为问题在于缓冲。

我目前解决这个问题的尝试感觉很复杂，因为这似乎是AVPlayer的一个相当基本的用例 - 我希望有一个更简单的解决方案来解决所有这些问题。不知怎的，我怀疑我在下面使用的缓冲播放器是非常必要的，但我的想法已经用完了。

以下是设置AVMutableComposition的主要代码：

// Build an AVAsset for each of the source URIs
- (void)prepareAssetsForSources:(NSArray *)sources
{
  NSMutableArray *assets = [[NSMutableArray alloc] init]; // the assets to be used in the AVMutableComposition
  NSMutableArray *offsets = [[NSMutableArray alloc] init]; // for tracking buffering progress
  CMTime currentOffset = kCMTimeZero;
  for (NSDictionary* source in sources) {
    bool isNetwork = [RCTConvert BOOL:[source objectForKey:@"isNetwork"]];
    bool isAsset = [RCTConvert BOOL:[source objectForKey:@"isAsset"]];
    NSString *uri = [source objectForKey:@"uri"];
    NSString *type = [source objectForKey:@"type"];

    NSURL *url = isNetwork ?
      [NSURL URLWithString:uri] :
      [[NSURL alloc] initFileURLWithPath:[[NSBundle mainBundle] pathForResource:uri ofType:type]];

    AVURLAsset *asset = [AVURLAsset URLAssetWithURL:url options:nil];
    currentOffset = CMTimeAdd(currentOffset, asset.duration);

    [assets addObject:asset];
    [offsets addObject:[NSNumber numberWithFloat:CMTimeGetSeconds(currentOffset)]];
  }
  _clipAssets = assets;
  _clipEndOffsets = offsets;
}

// Called with _clipAssets
- (AVPlayerItem*)playerItemForAssets:(NSMutableArray *)assets
{
  AVMutableComposition* composition = [AVMutableComposition composition];
  for (AVAsset* asset in assets) {
    CMTimeRange editRange = CMTimeRangeMake(CMTimeMake(0, 600), asset.duration);
    NSError *editError;

    [composition insertTimeRange:editRange
                         ofAsset:asset
                          atTime:composition.duration
                           error:&editError];
  }
  AVPlayerItem* playerItem = [AVPlayerItem playerItemWithAsset:composition];
  return playerItem; // this is used to initialize the main player
}

我最初的想法是：由于它使用香草AVPlayerItem快速缓冲，为什么不维护一个单独的缓冲播放器，依次加载每个资产（没有AVMutableComposition）来缓冲资产主要球员？

- (void)startBufferingClips
{
  _bufferingPlayerItem = [AVPlayerItem playerItemWithAsset:_clipAssets[0] 
                              automaticallyLoadedAssetKeys:@[@"tracks"]];
  _bufferingPlayer = [AVPlayer playerWithPlayerItem:_bufferingPlayerItem];
  _currentlyBufferingIndex = 0;
}

// called every 250 msecs via an addPeriodicTimeObserverForInterval on the main player
- (void)updateBufferingProgress
{
  // If the playable (loaded) range is within 100 milliseconds of the clip
  // currently being buffered, load the next clip into the buffering player.
  float playableDuration = [[self calculateBufferedDuration] floatValue];
  CMTime totalDurationTime = [self playerItemDuration :_bufferingPlayer];
  Float64 totalDurationSeconds = CMTimeGetSeconds(totalDurationTime);
  bool bufferingComplete = totalDurationSeconds - playableDuration < 0.1;
  float bufferedSeconds = [self bufferedSeconds :playableDuration];

  float playerTimeSeconds = CMTimeGetSeconds([_player currentTime]);
  __block NSUInteger playingClipIndex = 0;

  // find the index of _player's currently playing clip
  [_clipEndOffsets enumerateObjectsUsingBlock:^(id offset, NSUInteger idx, BOOL *stop) {
    if (playerTimeSeconds < [offset floatValue]) {
      playingClipIndex = idx;
      *stop = YES;
    }
  }];

  // TODO: if  bufferedSeconds - playerTimeSeconds <= 0, pause the main player

  if (bufferingComplete && _currentlyBufferingIndex < [_clipAssets count] - 1) {
    // We're done buffering this clip, load the buffering player with the next asset
    _currentlyBufferingIndex += 1;
    _bufferingPlayerItem = [AVPlayerItem playerItemWithAsset:_clipAssets[_currentlyBufferingIndex]
                                automaticallyLoadedAssetKeys:@[@"tracks"]];
    _bufferingPlayer = [AVPlayer playerWithPlayerItem:_bufferingPlayerItem];
  }
}

- (float)bufferedSeconds:(float)playableDuration {
  __block float seconds = 0.0; // total duration of clips already buffered
  if (_currentlyBufferingIndex > 0) {
    [_clipEndOffsets enumerateObjectsUsingBlock:^(id offset, NSUInteger idx, BOOL *stop) {
      if (idx + 1 >= _currentlyBufferingIndex) {
        seconds = [offset floatValue];
        *stop = YES;
      }
    }];
  }
  return seconds + playableDuration;
}

- (NSNumber *)calculateBufferedDuration {
  AVPlayerItem *video = _bufferingPlayer.currentItem;
  if (video.status == AVPlayerItemStatusReadyToPlay) {
    __block float longestPlayableRangeSeconds;
    [video.loadedTimeRanges enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
      CMTimeRange timeRange = [obj CMTimeRangeValue];
      float seconds = CMTimeGetSeconds(CMTimeRangeGetEnd(timeRange));
      if (seconds > 0.1) {
        if (!longestPlayableRangeSeconds) {
          longestPlayableRangeSeconds = seconds;
        } else if (seconds > longestPlayableRangeSeconds) {
          longestPlayableRangeSeconds = seconds;
        }
      }
    }];
    Float64 playableDuration = longestPlayableRangeSeconds;
    if (playableDuration && playableDuration > 0) {
      return [NSNumber numberWithFloat:longestPlayableRangeSeconds];
    }
  }
  return [NSNumber numberWithInteger:0];
}

最初看起来这就像一个魅力，但后来我切换到另一组测试片然后缓冲再次非常缓慢（缓冲播放器帮助，但还不够）。似乎加载到缓冲播放器中的资产的loadedTimeRange与loadedTimeRange内相同资产的AVMutableComposition不匹配：即使在loadedTimeRange之后加载到缓冲播放器中的每个项目的s表示整个资产已被缓冲，主要播放器的视频继续口吃（而音频无缝播放到最后）。同样，一旦主要播放器通过所有剪辑一次，重绕后回放是无缝的。

我希望这个问题的答案，无论它是什么，都将成为其他iOS开发人员试图实现这个基本用例的起点。谢谢！

编辑：自从我发布此问题以来，我为此做了以下解决方法。希望这可以帮助那些遇到麻烦的人。

我最终做的是维护两个缓冲播放器（两个AVPlayer s），它们开始缓冲前两个剪辑，然后继续移动到{{{后面的最低索引的无缓冲剪辑1}}表示已完成对当前剪辑的缓冲。我根据当前缓冲的剪辑和缓冲播放器的loadedTimeRanges以及一小部分进行了逻辑暂停/取消暂停播放。这需要一些簿记变量，但并不太复杂。

这就是缓冲播放器的初始化方式（我在这里省略了簿记逻辑）：

loadedTimeRanges

此外，我需要确保视频和音轨没有被合并，因为它们被添加到- (void)startBufferingClips { _bufferingPlayerItemA = [AVPlayerItem playerItemWithAsset:_clipAssets[0] automaticallyLoadedAssetKeys:@[@"tracks"]]; _bufferingPlayerA = [AVPlayer playerWithPlayerItem:_bufferingPlayerItemA]; _currentlyBufferingIndexA = [NSNumber numberWithInt:0]; if ([_clipAssets count] > 1) { _bufferingPlayerItemB = [AVPlayerItem playerItemWithAsset:_clipAssets[1] automaticallyLoadedAssetKeys:@[@"tracks"]]; _bufferingPlayerB = [AVPlayer playerWithPlayerItem:_bufferingPlayerItemB]; _currentlyBufferingIndexB = [NSNumber numberWithInt:1]; _nextIndexToBuffer = [NSNumber numberWithInt:2]; } else { _nextIndexToBuffer = [NSNumber numberWithInt:1]; } }，因为这显然干扰了缓冲（可能它们没有注册为相同视频/音频轨道就像缓冲播放器正在加载的那样，因此没有收到新数据）。以下是从AVMutableComposition s：

数组构建AVMutableComposition的代码

NSAsset

使用这种方法，在主播放器上使用- (AVPlayerItem*)playerItemForAssets:(NSMutableArray *)assets { AVMutableComposition* composition = [AVMutableComposition composition]; AVMutableCompositionTrack *compVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; AVMutableCompositionTrack *compAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid]; CMTime timeOffset = kCMTimeZero; for (AVAsset* asset in assets) { CMTimeRange editRange = CMTimeRangeMake(CMTimeMake(0, 600), asset.duration); NSError *editError; NSArray *videoTracks = [asset tracksWithMediaType:AVMediaTypeVideo]; NSArray *audioTracks = [asset tracksWithMediaType:AVMediaTypeAudio]; if ([videoTracks count] > 0) { AVAssetTrack *videoTrack = [videoTracks objectAtIndex:0]; [compVideoTrack insertTimeRange:editRange ofTrack:videoTrack atTime:timeOffset error:&editError]; } if ([audioTracks count] > 0) { AVAssetTrack *audioTrack = [audioTracks objectAtIndex:0]; [compAudioTrack insertTimeRange:editRange ofTrack:audioTrack atTime:timeOffset error:&editError]; } if ([videoTracks count] > 0 || [audioTracks count] > 0) { timeOffset = CMTimeAdd(timeOffset, asset.duration); } } AVPlayerItem* playerItem = [AVPlayerItem playerItemWithAsset:composition]; return playerItem; }时缓冲可以很好地运行，至少在我的设置中是这样。

使用AVPlayer和AVMutableComposition

0 个答案: