AVPlayer.currentItem.loadedTimeRanges

// subscribe for KVO somewhere  
[_player addObserver:self
          forKeyPath:@"currentItem.loadedTimeRanges"
             options:NSKeyValueObservingOptionNew
             context:nil];

...

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
                        change:(NSDictionary *)change context:(void *)contex
{
    ...

    if (object == _player && [keyPath isEqualToString:@"currentItem.loadedTimeRanges"])
    {
        NSArray *timeRanges = (NSArray*)[change objectForKey:NSKeyValueChangeNewKey];
        if (timeRanges && [timeRanges count])
        {
            CMTimeRange timerange;
            NSValue* val = [timeRanges objectAtIndex:0];
            [val getValue:&timerange];
            
            float currentBufferDuration = CMTimeGetSeconds(CMTimeAdd(timerange.start, timerange.duration));
            CMTime duration = _player.currentItem.asset.duration;
            float seconds = CMTimeGetSeconds(duration);
            float hours=seconds/3600;
            NSLog(@"Movie takes %.2f hours", hours);
            
            if (currentBufferDuration == seconds)
            {
                // Ready to play.
            }
        }
    }
}