Correct progress of an offline download with AVAssetDownloadURLSession

Question

I'm downloading offline video thanks to AVAssetDownloadURLSession, AVAssetDownloadDelegate for iOS 11 using makeAssetDownloadTask(...) and aggregateAssetDownloadTask(...) method.

Everything works but I just want to let the users know the progress of each download as accurately as possible.

To do so I use:

- urlSession(_ session: URLSession, assetDownloadTask: AVAssetDownloadTask, didLoad timeRange: CMTimeRange, totalTimeRangesLoaded loadedTimeRanges: [NSValue], timeRangeExpectedToLoad: CMTimeRange)

- urlSession(_ session: URLSession, aggregateAssetDownloadTask: AVAggregateAssetDownloadTask, didLoad timeRange: CMTimeRange, totalTimeRangesLoaded loadedTimeRanges: [NSValue], timeRangeExpectedToLoad: CMTimeRange, for mediaSelection: AVMediaSelection)

With these methods I'm able to calculate the download progress of the video and each tracks (audio/subtitle) separately. So I assume the video is 70% of the download and for the tracks it's 30% divided by the number of tracks. I store the download progress of each items in a temporary dictionary (multiplied by their ratio) and I add each progress for a download to have a global representation.

In the end it works fine but it's not as smooth as expected. For example I spend 3min to download the content but if the weight of a track is light, the progress will jump from 70% to 85% in 1sec (if I have 2 tracks to download) and slow down right after. I would like to have a global progress.

I definitely not happy with this solution but I currently did not find another solution.

Do some of you have any ideas/solutions?

Thanks guys

Answer 1

Solution

First of all, this is just my case, you should update the method for your needs.

In my scenario, as a most complicated array example I have something like this:

[English(soun),Turkish(soun),English(sbtl),Turkish(sbtl)]

We'll give 80 percent for Audio all audios, and 20 percent for all subtitles.

The total calculation formula must be something like this:

(100*(0,80/2))+(100*(0,80/2))+(100*(0,20/2))+(100(0,20/2))

We need an enum for representing AVMediaType:

// AVMediaType
enum MediaType: String {
    // Sound
    case soun
        
    // Subtitle
    case sbtl
      
    // Closed Caption
    // case clcp // Removed for simplifying the example.
}

Also, we'll need a Dictionary to handle Asset Download Progress:

var totalDownloadProgressForAsset = [String: Double]()

And here is the method:

public func getTotalProgress() -> Double {
    var result = 0.0
    let soundMultiplier          = 0.80
    let subtitleMultiplier       = 0.20
    var soundCount = 0
    var subtitleCount  = 0
    
    for (key, _) in totalDownloadProgressForAsset {
        let mediaTypeKey = String(key.suffix(4))
        let type = MediaType(rawValue: mediaTypeKey)
        
        switch type {
        case .soun:
            soundCount += 1
        case .sbtl:
            subtitleCount += 1
        case .none:
            break
        }
    }
                    
    for (key, value) in totalDownloadProgressForAsset {
        let mediaTypeKey = String(key.suffix(4))
        let type = MediaType(rawValue: mediaTypeKey)
        
        switch type {
        case .soun:
            result += Double(value*(soundMultiplier/Double(soundCount)))
        case .sbtl:
            result += Double(value*(subtitleMultiplier/Double(subtitleCount)))
        case .none:
            break
        }
    }
    
    return result
}

Of course, we can write this differently, this is just for example.

Feel free to ask anything about it.