Hello, I have implemented Low-Latency Frame Interpolation using the VTFrameProcessor framework, based on the sample code from https://developer.apple.com/kr/videos/play/wwdc2025/300. It is currently working well for both LIVE and VOD streams. However, I have a few questions regarding the lifecycle management and synchronization of this feature: 1. Common Questions (Applicable to both Frame Interpolation & Super Resolution) 1.1 Dynamic Toggling Do you recommend enabling/disabling these features dynamically during playback? Or is it better practice to configure them only during the initial setup/preparation phase? If dynamic toggling is supported, are there any recommended patterns for managing VTFrameProcessor session lifecycle (e.g., startSession / endSession timing)? 1.2 Synchronization Method I am currently using CADisplayLink to fetch frames from AVPlayerItemVideoOutput and perform processing. Is CADisplayLink the recommended approach for real-time frame acquisition with VTFrameProcessor? If the feature needs to be toggled on/off during active playback, are there any concerns or alternative approaches you would recommend? 1.3 Supported Resolution/Quality Range What are the minimum and maximum video resolutions supported for each feature? Are there any aspect ratio restrictions (e.g., does it support 1:1 square videos)? Is there a recommended resolution range for optimal performance and quality? 2. Frame Interpolation Specific Questions 2.1 LIVE Stream Support Is Low-Latency Frame Interpolation suitable for LIVE streaming scenarios where latency is critical? Are there any special considerations for LIVE vs VOD? 3. Super Resolution Specific Questions 3.1 Adaptive Bitrate (ABR) Stream Support In ABR (HLS/DASH) streams, the video resolution can change dynamically during playback. Is VTLowLatencySuperResolutionScaler compatible with ABR streams where resolution changes mid-playback? If resolution changes occur, should I recreate the VTLowLatencySuperResolutionScalerConfiguration and restart the session, or does the API handle this automatically? 3.2 Small/Square Resolution Issue I observed that 144x144 (1:1 square) videos fail with error:   "VTFrameProcessorErrorDomain Code=-19730: processWithSourceFrame within VCPFrameSuperResolutionProcessor failed" However, 480x270 (16:9) videos work correctly. minimumDimensions reports 96x96, but 144x144 still fails. Is there an undocumented restriction on aspect ratio or a practical minimum resolution? 3.3 Scale Factor Selection supportedScaleFactors returns [2.0, 4.0] for most resolutions. Is there a recommended scale factor for balancing quality and performance? Are there scenarios where 4.0x should be avoided? The documentation on this specific topic seems limited, so I would appreciate any insights or advice. Thank you.

Hello, I am developing a custom player SDK based on AVPlayer. While testing LL-HLS streams, I intermittently encounter the following error: Error Domain=CoreMediaErrorDomain Code=-12880 Since I cannot find documentation for this specific code, could you please clarify its meaning? Specifically, I would like to know if this is a critical error that disrupts playback, or if it is just a warning that can be safely ignored. Any insights would be appreciated. Thank you.

Hi, Has anyone been able to protect the audio part of FairPlay protected content from being captured as part of screen recording on Safari/iOS (PWA and/or online web app)? We have tried many things but could not prevent the audio from being recorded. Same app and content on Safari/Mac does not allow audio to be recorded. Any tips?

Hello, I am currently developing a live streaming application using AVPlayer to play LL-HLS (Low-Latency HLS) content. During our testing phase, we consistently encountered the following error in the logs: CoreMediaErrorDomain Code=-15517 The challenge we are facing is that the error description is quite vague. It only provides cryptic messages such as "Key not found" or "No value information," which makes it extremely difficult to identify the root cause or perform a deep-dive analysis. I have searched through the official Apple Developer documentation and technical notes, but I couldn’t find any specific reference to what Code -15517 signifies in the context of LL-HLS or CoreMedia. Regarding this issue, I have the following questions: What is the specific meaning of this error code (-15517)? Does it relate to missing tags in the HLS manifest, or is it an internal state issue within the AVPlayer stack? Specifically, I would like to know if this is a critical error that disrupts playback, or if it is just a warning that can be safely ignored. Is there any additional logging or debugging tool you would recommend to further investigate "Key not found" issues in LL-HLS? Any insights or guidance from the community or Apple engineers would be greatly appreciated. Thank you in advance for your help.

Hi everyone, Our team is encountering a reproducible crash when using VTLowLatencyFrameInterpolation on iOS 26.3 while processing a live LL-HLS input stream. 🤖 Environment Device: iPhone 16 OS: iOS 26.3 Xcode: Xcode 26.3 Framework: VideoToolbox 💥 Crash Details The application crashes with the following fatal error: Fatal error: Swift/ContiguousArrayBuffer.swift:184: Array index out of range The stack trace highlights the following: VTLowLatencyFrameInterpolationImplementation processWithParameters:frameOutputHandler: Called from VTFrameProcessor.process(parameters:) Here is the simplified implementation block where the crash occurs. (Note: PrismSampleBuffer and PrismLLFIError are our internal custom wrapper types). // Create `VTFrameProcessorFrame` for the source (previous) frame. let sourcePTS = sourceSampleBuffer.presentationTimeStamp var sourceFrame: VTFrameProcessorFrame? if let pixelBuffer = sourceSampleBuffer.imageBuffer { sourceFrame = VTFrameProcessorFrame(buffer: pixelBuffer, presentationTimeStamp: sourcePTS) } // Validate the source VTFrameProcessorFrame. guard let sourceFrame else { throw PrismLLFIError.missingImageBuffer } // Create `VTFrameProcessorFrame` for the next frame. let nextPTS = nextSampleBuffer.presentationTimeStamp var nextFrame: VTFrameProcessorFrame? if let pixelBuffer = nextSampleBuffer.imageBuffer { nextFrame = VTFrameProcessorFrame(buffer: pixelBuffer, presentationTimeStamp: nextPTS) } // Validate the next VTFrameProcessorFrame. guard let nextFrame else { throw PrismLLFIError.missingImageBuffer } // Calculate interpolation intervals and allocate destination frame buffers. let intervals = interpolationIntervals() let destinationFrames = try framesBetween(firstPTS: sourcePTS, lastPTS: nextPTS, interpolationIntervals: intervals) let interpolationPhase: [Float] = intervals.map { Float($0) } // Create VTLowLatencyFrameInterpolationParameters. // This sets up the configuration required for temporal frame interpolation between the previous and current source frames. guard let parameters = VTLowLatencyFrameInterpolationParameters( sourceFrame: nextFrame, previousFrame: sourceFrame, interpolationPhase: interpolationPhase, destinationFrames: destinationFrames ) else { throw PrismLLFIError.failedToCreateParameters } try await send(sourceSampleBuffer) // Process the frames. // Using progressive callback here to get the next processed frame as soon as it's ready, // preventing the system from waiting for the entire batch to finish. for try await readOnlyFrame in self.frameProcessor.process(parameters: parameters) { // Create an interpolated sample buffer based on the output frame. let newSampleBuffer: PrismSampleBuffer = try readOnlyFrame.frame.withUnsafeBuffer { pixelBuffer in try PrismLowLatencyFrameInterpolation.createSampleBuffer(from: pixelBuffer, readOnlyFrame.timeStamp) } // Pass the newly generated frame to the output stream. try await send(newSampleBuffer) } 🙋 Questions Are there any known limitations or bugs regarding VTLowLatencyFrameInterpolation when handling live 60fps streams? Are there any undocumented constraints we should be aware of regarding source/previous frame timing, pixel buffer attributes, or how destinationFrames and interpolationPhase arrays must be allocated? Is a "warm-up" sequence recommended after startSession() before making the first process(parameters:) call?

Hi, I’m trying to better understand how AVAssetDownloadConfiguration selects video variants when downloading HLS content for offline playback. Suppose I have an HLS master playlist (.m3u8) that contains several video variants defined with #EXT-X-STREAM-INF. For example, the master playlist may contain multiple video streams like this: Same resolution, different BANDWIDTH Or different resolutions (for example 720p, 1080p, etc.) My question is: How many video variants are actually downloaded when using AVAssetDownloadConfiguration without specifying any variantQualifiers? In other words: If the master playlist contains multiple video variants, will the download task fetch only one variant, or multiple variants? Does the behavior differ depending on whether the variants differ only by BANDWIDTH or also by RESOLUTION? What I observed in testing In my tests, I always end up with only one video variant downloaded, specifically the one with the highest BANDWIDTH parameter. In the m3u8 files I tested, all video variants had identical parameters (resolution, codec, frame rate, etc.) and differed only by the BANDWIDTH attribute in the master playlist. However, when inspecting the downloaded .movpkg, I noticed something interesting in boot.xml. It lists two video streams: one with complete="true" (the one with highest bandwidth) another with complete="no" (the one with lowest bandwidth) I actually had 3 video streams listed in m3u8, but the one with middle bandwidth wasn't listed in boot.xml file at all. There are also additional streams for audio and subtitles in boot.xml file. This made me wonder whether the system initially attempts to download another video variant (possibly a lower bitrate one), but then switches to the highest-quality variant and only completes that one. Additional question about variantQualifiers If I provide a predicate such as: NSPredicate(format: "peakBitRate > 0") which should theoretically match all variants, will the download task attempt to download all matching video variants, or will it still select only one? Summary So the main questions are: Without variantQualifiers, does AVAssetDownloadConfiguration always download a single video variant, and if so, how is it chosen? Does the behavior differ if variants have different resolutions vs only different bitrates? When a predicate matches multiple variants, can multiple video variants actually be downloaded in a single .movpkg? Why might boot.xml list multiple video streams when only one appears to be fully downloaded? Any clarification on the intended behavior would be greatly appreciated. Thanks!

Summary On iOS 26, HLS alternate audio track selection behaves inconsistently on both VOD and live streams: the French track falls back to the DEFAULT=YES (English) track after manual selection, and in some cases switching to a non-default track appears to work but it is then impossible to switch back to English. Environment iOS version: 26 Players affected: native Safari on iOS 26 and THEOplayer (issue also reproducible on THEOplayer's own demo page) Stream type: HLS/CMAF with demuxed alternate audio renditions (CMFC container) Affected stream types: both VOD and live streaming Issue NOT present on iOS 17/18 Manifest #EXTM3U #EXT-X-VERSION:4 #EXT-X-INDEPENDENT-SEGMENTS #EXT-X-STREAM-INF:BANDWIDTH=8987973,AVERAGE-BANDWIDTH=8987973,VIDEO-RANGE=SDR,CODECS="avc1.640028",RESOLUTION=1920x1080,FRAME-RATE=29.970,AUDIO="program_audio" video_1080p.m3u8 #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="program_audio",LANGUAGE="en",ASSOC-LANGUAGE="en",NAME="English",AUTOSELECT=YES,DEFAULT=YES,CHANNELS="2",URI="audio_ENG.m3u8" #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="program_audio",LANGUAGE="de",ASSOC-LANGUAGE="de",NAME="Deutsch",AUTOSELECT=YES,DEFAULT=NO,CHANNELS="2",URI="audio_DEU.m3u8" #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="program_audio",LANGUAGE="fr",ASSOC-LANGUAGE="fr",NAME="Francais",AUTOSELECT=YES,DEFAULT=NO,CHANNELS="2",URI="audio_FRA.m3u8" Steps to Reproduce Load the HLS manifest (VOD or live) in Safari on iOS 26, or in any AVFoundation-backed player Start playback — English plays correctly as DEFAULT Manually select "Francais" from the audio track selector Observe that English audio continues playing (French does not play) In a separate scenario: manually select "Deutsch" — German plays correctly Attempt to switch back to English — English does not resume; audio remains on the previously selected track Expected behavior Selecting any track should immediately switch to that language Switching back to English (DEFAULT=YES) should work at any time Behavior should be consistent across VOD and live streams Actual behavior Two distinct anomalies observed, reproducible on both VOD and live streams, in both native Safari and THEOplayer: French-specific fallback: selecting the French track causes playback to fall back to English. This does not happen with German. Cannot return to English: in cases where a non-default track plays correctly, attempting to switch back to the DEFAULT=YES track (English) fails — the previous non-default track continues playing. The fact that the issue reproduces in native Safari confirms this is an AVFoundation/WebKit-level regression, not a third-party player bug. What we have already verified and ruled out LANGUAGE codes are BCP-47 compliant (en, fr, de) ✓ EXT-X-VERSION:4 is present ✓ Audio codec removed from STREAM-INF CODECS (video-only) ✓ ASSOC-LANGUAGE attribute added matching LANGUAGE value ✓ Container metadata verified via ffprobe: mdhd box correctly contains language tags (e.g. "fra") ✓ Audio segment content verified via ffplay: correct audio in each language file ✓ French audio source file contains correct French audio content ✓ Issue reproduces in native Safari on iOS 26, confirming it is not a THEOplayer-specific bug Issue does NOT reproduce on iOS 17/18 with the same manifest and segments Additional notes The VOD stream is packaged with AWS MediaConvert, CMAF output group, SEGMENTED_FILES, AAC-LC codec (mp4a.40.2), 128kbps, 48kHz stereo. English uses AudioTrackType ALTERNATE_AUDIO_AUTO_SELECT_DEFAULT; French and German use ALTERNATE_AUDIO_AUTO_SELECT. The live stream uses AWS MediaPackage with a similar CMAF/HLS output configuration. Please advise whether this is a known regression in AVFoundation on iOS 26 and whether a fix is planned.

Hello there, Our application has HLS VOD download option. Users can download VOD which has DRM protection and watch content when device is offline. We use aggregateAssetDownloadTask to download HLS VOD. We want to resume download after Wifi/LTE change but it does not resume. Download is starting from beginning. We use some token algorithms to start download. That's why, our playlist url and chunks urls may change. But playlist and chunk urls' content is unique. If user start to download via Wifi and changed to LTE. Download request responds 403 Forbidden because of some token algorithms after some time func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) AVAssetDownloadDelegate function triggered by system. If we resume it does not resume at this point. It is starting from beginning if we start new download process for same content. Is there any way to resume unfinished HLS Download processes? Thanks

Hi, I'm currently experiencing issues with HLS streams created by FFmpeg running on Safari. When I pass the stream to the mediastreamvalidator tool and then run hlsreport on the output, I get a critical error reported: Media Entry discontinuity value does not match previous playlist for MEDIA-SEQUENCE 1 If I let the stream finish (it's a live stream from an IoT device) and then perform the stream validation again I no longer receive the critical error. My assumption is that this critical error is contributing to the HLS stall on iOS. I have also noticed that if I let the stream continue and then re-load the video control in Safari the stream starts Is there a resource with explanations or remediation paths relevant to the possible output of the hlsreport? My m3u8 output looks like this (I have redacted the server host) #EXTM3U #EXT-X-VERSION:6 #EXT-X-TARGETDURATION:2 #EXT-X-MEDIA-SEQUENCE:1 #EXT-X-PLAYLIST-TYPE:EVENT #EXT-X-INDEPENDENT-SEGMENTS #EXT-X-DISCONTINUITY #EXTINF:2.000000, https://redacted.com/segment-00001.ts #EXTINF:2.000011, https://redacted.com/segment-00002.ts #EXTINF:2.000011, https://redacted.com/segment-00003.ts #EXTINF:2.000011, https://redacted.com/segment-00004.ts #EXTINF:2.000011, #EXT-X-ENDLIST Thanks for any advice or guidance possible - if I can provide isolated code snippets I will do. Andy