如何通知我已确定电影不是电影？

Question

I'm writing a Mac app that plays MPEG-4 movies using AVPlayer.

My app supports both local movies and movies from the internet, via an “Open Location” dialog. In the latter case, when the user enters a URL and presses the OK button, my app opens the URL as a document.

Local files are easy—Launch Services will tell Finder, Dock, etc. not to light my app up for any local file that isn't a .mp4 or similar. If the user forces my app to open some random file (eg, by holding down ⌘ when dragging it onto my app), that's their own fault.

Non-local (eg, internet) URLs are the problem. If I supply a URL that doesn't lead to an MPEG-4, I need to show an alert and close the document.

Of course, I'm not downloading the URL myself; I just hand it to AVPlayer.

So I need a way to be notified by my AVPlayer that what I've given it is not a movie.

• I've tried observing the player's status . That gets set to AVPlayerStatusReadyToPlay .
• I've tried observing the player's currentItem 's tracks . At least on Lion, for an invalid movie, the item's tracks never changes. (This stands to reason—the only reason it would change would be tracks coming in, which is, by definition, impossible for a non-movie.)
• I can't just check tracks when status changes, because that may not be set yet (on Mavericks, status changes before tracks ).

So, how can I be notified by my AVPlayer that it has conclusively determined that what the URL refers to is not anything it can play?

Answer 1

It's absolutely not definitive, but in my experience, when the player's status becomes AVPlayerStatusReadyToPlay , you can inspect the playable property of asset of the player's currentItem . If playable is YES , you can assume the URL led to a viable MP4. If not, you can assume it did not.

- (void) observeValueForKeyPath:(NSString*)keyPath
                       ofObject:(id)object
                         change:(NSDictionary*)change
                        context:(void*)context
{
    if( [keyPath isEqualToString:@"status"] ) {
        if( self.player.status == AVPlayerStatusReadyToPlay && 
            self.player.currentItem.asset.playable ) {
            [self.playerView.player play];
        }
        else {
            // TODO: show an error dialog here.
            [self.window close];
        }
    }
}

I've code similar to the above in one of my apps, and it seems to work as expected in every case I've tried. I can whip up a test app with it if you like.