AVURLAsset load webvtt file

Question

I am trying to use AVURLAsset to load a webvtt file.

Below is my code.

    NSString *urlAddress = @"http://somewhere/some.vtt";
    NSURL *urlStream = [[NSURL alloc] initWithString:urlAddress];
    AVAsset *avAsset = [AVURLAsset URLAssetWithURL:urlStream options:nil];

    NSArray *requestKeys = [NSArray arrayWithObjects:@"tracks",@"playable",nil];
    [avAsset loadValuesAsynchronouslyForKeys:requestKeys completionHandler:^{
    dispatch_async(dispatch_get_main_queue(),^{

        //complete block here
        AVKeyValueStatus status =[avAsset statusOfValueForKey:@"tracks" error:nil];
        if(status == AVKeyValueStatusLoaded) {

            //loaded block !
            //Question 1
            CMTime assetTime = [avAsset duration];
            Float64 duration = CMTimeGetSeconds(assetTime);
            NSLog(@"%f", duration);

            //Question 2
            AVMediaSelectionGroup *subtitle = [avAsset mediaSelectionGroupForMediaCharacteristic: AVMediaCharacteristicLegible];
            NSLog(@"%@", subtitle);
        }
        else {
            //don’t load block ! 
        }
    });
}];

Question 1: It always go into the "Loaded Block", but I find the avAsset's duration is not complete, that means the data is not loaded? How should I modify it?

Question 2: I am trying to use it to my avplayer's subtitle, but the AVMediaSelectionGroup is always null. What should I do?

Hi is this working, I tried this but its not working ? any idea? — Yohan, Feb 22 '16 at 08:41

score 0 · Answer 1 · answered Oct 14 '15 at 02:49

0

For question 1, add duration to your keys:

NSArray *requestKeys = @[@"tracks",@"playable", @"duration"];

answered Oct 14 '15 at 02:49

Rhythmic Fistman

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Hi, thanks for your reply. I add it but the result is the same. – Leon Shiu Oct 14 '15 at 03:14
oh no. have you tried opening the URL in Mobile Safari? – Rhythmic Fistman Oct 14 '15 at 03:15
that sounds wrong. do you have a public link to the file? – Rhythmic Fistman Oct 14 '15 at 03:41
Ok - I see, what are you trying to do? Duration works for me, but `AVMediaSelectionGroup` only seems to be available for subtitles inside movies. – Rhythmic Fistman Oct 15 '15 at 01:20
the duration you got is ? – Leon Shiu Oct 15 '15 at 02:38
3978.03s or 1hr 6minutes and 18seconds – Rhythmic Fistman Oct 15 '15 at 02:41
It should be 6951.053 – Leon Shiu Oct 15 '15 at 02:49

score 0 · Answer 2 · edited May 23 '17 at 12:08

I've posted a solution over here: https://stackoverflow.com/a/37945178/171933 Basically you need to use an AVMutableComposition to join the video with the subtitles and then play back that composition.

About your second question: mediaSelectionGroupForMediaCharacteristic seems to only be supported when these "characteristics" are already baked into either the media file or your m3u8 stream, according to this statement by an Apple engineer (bottom of the page).

AVURLAsset load webvtt file

2 Answers2