探索 AVFoundation 中的 HLS 变体

0:40 - HLS Master Playlist

#EXTM3U
#EXT-X-VERSION:7
#EXT-X-INDEPENDENT-SEGMENTS

#EXT-X-MEDIA:TYPE=AUDIO,NAME="English",GROUP-ID="stereo",LANGUAGE="en",DEFAULT=YES, AUTOSELECT=YES,CHANNELS="2",URI="en_stereo.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,NAME="French",GROUP-ID="stereo",LANGUAGE="fr",DEFAULT=NO, AUTOSELECT=YES,CHANNELS="2",URI="fr_stereo.m3u8"

#EXT-X-MEDIA:TYPE=AUDIO,NAME="English",GROUP-ID="atmos",LANGUAGE="en",DEFAULT=YES, AUTOSELECT=YES,CHANNELS="16/JOC",URI="en_atmos.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,NAME="French",GROUP-ID="atmos",LANGUAGE="fr",DEFAULT=NO, AUTOSELECT=YES,CHANNELS="16/JOC",URI="fr_atmos.m3u8"

#EXT-X-STREAM-INF:BANDWIDTH=14516883,VIDEO-RANGE=SDR,CODECS="avc1.64001f,mp4a.40.5", AUDIO="stereo",FRAME-RATE=23.976,RESOLUTION=1920x1080
sdr_variant.m3u8

#EXT-X-STREAM-INF:BANDWIDTH=34516883,VIDEO-RANGE=PQ,CODECS="dvh1.05.06,ec-3", AUDIO="atmos",FRAME-RATE=23.976,RESOLUTION=3840x1920
dovi_variant.m3u8

3:38 - Peak bitrate cap predicate

let peakBitRateCap = NSPredicate(format: "peakBitRate < 5000000")

let peakBitRateCapQualifier = AVAssetVariantQualifier(predicate: peakBitRateCap)

3:55 - HDR predicate

let hdrOnlyPredicate = NSPredicate(format: "videoAttributes.videoRange == %@", argumentArray: [AVVideoRange.pq])

let hdrOnlyQualifier = AVAssetVariantQualifier(predicate: hdrOnlyPredicate)

4:46 - Content configuration

let variantPref = AVAssetVariantQualifier(predicate: NSPredicate(format: "videoAttributes.videoRange == %@ && peakBitRate < 5000000", argumentArray: [AVVideoRange.pq]))

let myMediaSelections : [AVMediaSelection] = [enAudioMS, frAudioMS, enLegibleMS] //English, French audio and English subtitle renditions 

let contentConfig = AVAssetDownloadContentConfiguration()

contentConfig.variantQualifiers = [variantPref]

contentConfig.mediaSelections = myMediaSelections

6:29 - Download configuration

let asset = AVURLAsset(url: URL(string: "http://example.com/master.m3u8")!)
let dwConfig = AVAssetDownloadConfiguration(asset: asset, title: "my-title")

/* Primary content config */
let varPref = NSPredicate(format: "videoAttributes.videoRange == %@ && peakBitRate < 5000000", argumentArray: [AVVideoRange.pq])
let varQf = AVAssetVariantQualifier(predicate: varPref)

dwConfig.primaryContentConfiguration.variantQualifiers = [varQf]
dwConfig.primaryContentConfiguration.mediaSelections = [enAudioMS, frAudioMS, enLegibleMS] //English, French audio and English subtitle renditions 

/* Aux content config */
let auxVarPref = NSPredicate(format: "%d IN audioAttributes.formatIDs", argumentArray: [kAudioFormatAppleLossless])
let auxVarQf = AVAssetVariantQualifier(predicate: auxVarPref)

let auxContentConfig = AVAssetDownloadContentConfiguration()
auxContentConfig.variantQualifiers = [auxVarQf]
auxContentConfig.mediaSelections = [enAudioMS] //english audio
dwConfig.auxiliaryContentConfigurations = [auxContentConfig]

dwConfig.optimizesAuxiliaryContentConfigurations = true

7:42 - Download task

let myAssetDownloadDelegate = MyDownloadDelegate()
let avurlsession = AVAssetDownloadURLSession(configuration: URLSessionConfiguration.background(withIdentifier: "my-background-session"), assetDownloadDelegate: myAssetDownloadDelegate, delegateQueue: OperationQueue.main)

let asset = AVURLAsset(url: URL(string: "http://example.com/master.m3u8")!)
let dwConfig = AVAssetDownloadConfiguration(asset: asset, title: “my-title”)

...

let downloadTask = avurlsession.makeAssetDownloadTask(downloadConfiguration: dwConfig)

downloadTask.resume()

let progress = downloadTask.progress

8:10 - Direct variant selection

/* Example for direct variant selection */

let asset = AVURLAsset(url: URL(string: "http://example.com/master.m3u8")!)
let dwConfig = AVAssetDownloadConfiguration(asset: asset, title: "my-title")

/* Primary content config */
let myVariant : AVAssetVariant = ...
let myMediaSelections : [AVMediaSelection] = ...

let variantQf = AVAssetVariantQualifier(variant: myVariant)

dwConfig.primaryContentConfiguration.variantQualifiers = [variantQf]
dwConfig.primaryContentConfiguration.mediaSelections = myMediaSelections

/* Aux content config */
let myAuxVariant : AVAssetVariant = ...
let myAuxMediaSelections : [AVMediaSelection] = ...

let auxVariantQf = AVAssetVariantQualifier(variant: myAuxVariant)

let auxContentConfig = AVAssetDownloadContentConfiguration()
auxContentConfig.variantQualifiers = [auxVariantQf]
auxContentConfig.mediaSelections = myAuxMediaSelections
dwConfig.auxiliaryContentConfigurations = [auxContentConfig]