How to troubleshoot HLS live stream in iOS

If you’re working with HLS live streams on iOS, you’ve probably run into a few bumps along the way. Maybe the stream keeps buffering, segments aren’t loading right, or there’s unexpected lag.  

Don’t worry, this guide breaks down common issues like these and gives you straightforward tips to troubleshoot and fix them, so you can keep your streams running smoothly and your users happy.

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Common issues in HLS streaming

When it comes to delivering a seamless streaming experience, HTTP Live Streaming (HLS) can present several technical challenges that developers need to address proactively. Here’s an in-depth look at the most common issues you may encounter, along with some technical insights on their origins and potential solutions.

• Buffering and latency: Frequent buffering can ruin the viewing experience and is typically caused by network fluctuations or bitrate mismatches. Frequent buffering is often the result of network fluctuations or bitrate mismatches, where the player’s requested bitrate doesn’t match the network's capacity. Solutions include implementing adaptive bitrate streaming to dynamically adjust the quality based on current network conditions and optimizing segment duration to reduce wait times between downloads.
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• Playback errors:  Most commonly seen Playback errors such as  AVPlayerItemFailedToPlayToEndTimeError or NSURLErrorNetworkConnectionLost can arise when HLS segments are missing, improperly formatted, or temporarily inaccessible. These errors often stem from server-side issues, like incomplete segment uploads or network interruptions. To mitigate these issues, ensure that your server provides better error handling, retries for segment delivery, and regularly monitors segment availability.
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• Quality drops: Abrupt quality changes often result from inefficient bitrate switching or low-resolution segments. Sudden drops in video quality can disrupt the viewing experience, typically caused by inefficient bitrate switching or low-resolution fallback segments. This often happens if the HLS manifest doesn’t include sufficient high-quality options or if bandwidth estimation is inaccurate. You can minimize quality drops by fine-tuning your bitrate ladder, ensuring your HLS manifest includes multiple quality levels, and improving your bandwidth estimation algorithms.
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• Audio/Video sync: Out-of-sync audio and video can stem from encoding issues or segment inconsistencies. Desynchronization between audio and video can be jarring for viewers and usually arises from encoding issues or inconsistencies in segment timing. This may happen if audio and video are encoded at different bitrates or if segment timestamps are mismatched. To address this, ensure consistent encoding parameters across streams, use synchronized timestamps, and validate segment alignment before pushing content to production.

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Troubleshooting steps for iOS  

Here’s a structured approach to troubleshooting HLS streams in iOS:

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1. Check network conditions

HLS (HTTP Live Streaming) uses adaptive bitrate streaming to provide a smoother viewing experience across various network conditions. This approach dynamically adjusts video quality to match the viewer's available bandwidth and device capability, reducing buffering and maintaining playback even on fluctuating networks.

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Swift

1import Network 
2
3let monitor = NWPathMonitor() 
4monitor.pathUpdateHandler = { path in 
5    if path.status == .satisfied { 
6        print("Network available") 
7    } else { 
8        print("Network unavailable") 
9    } 
10} 
11let queue = DispatchQueue(label: "NetworkMonitor") 
12monitor.start(queue: queue) 

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If the network is weak, consider implementing a custom solution to display a message to the user or adapt the stream quality accordingly.

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2. Use AVPlayer diagnostics for playback errors

When playback issues arise, the AVPlayer in iOS provides valuable error messages that can help identify the cause. By listening to notifications from AVPlayerItem, you can capture detailed error information and respond accordingly to improve the user experience.

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Swift

1NotificationCenter.default.addObserver(self, selector: #selector(handlePlaybackError), name: .AVPlayerItemFailedToPlayToEndTime, object: player.currentItem) 
2
3@objc func handlePlaybackError(notification: NSNotification) { 
4    if let error = notification.userInfo?[AVPlayerItemFailedToPlayToEndTimeErrorKey] as? Error { 
5        print("Playback error: \(error.localizedDescription)") 
6    } 
7} 

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Capturing these errors allows you to identify if the issue is related to the player, the network, or the content source.

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3. Validate the HLS playlist

One of the most frequent causes of playback issues in HLS streaming is an improperly structured playlist file, also known as the .m3u8 file. This file acts as a roadmap for the HLS player, guiding it to the appropriate media segments for playback. Ensuring the playlist is well-formed and error-free is essential for a smooth streaming experience. Here’s how to validate an HLS playlist and what to look out for.

• The playlist is properly formatted.
• All segment URLs are accessible.
• Ensure Consistent Segment Durations.
• Validate playlists with Tools.
• Check Playlist Compatibility with Different Network Conditions.
• Automated Monitoring.

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4. Monitor buffer status

Understanding buffer status is essential for diagnosing buffering and playback issues, as it allows you to see when the player is waiting for more data and when it's actively playing or paused. In iOS, the AVPlayer class provides the timeControlStatus property, which helps you track the player’s state—whether it’s playing, paused, or buffering. Here’s how to use this property to monitor and handle buffer-related issues in your HLS stream.

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Swift

1player.addObserver(self, forKeyPath: "timeControlStatus", options: [.old, .new], context: nil) 
2
3override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) { 
4    if keyPath == "timeControlStatus" { 
5        if player.timeControlStatus == .waitingToPlayAtSpecifiedRate { 
6            print("Buffering...") 
7        } else if player.timeControlStatus == .playing { 
8            print("Playing") 
9        } 
10    } 
11} 

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5. Optimize bitrate switching

Poorly configured bitrates in your HLS manifest file can lead to abrupt quality drops, which disrupt the viewing experience and can frustrate users. To maintain smooth playback, ensure that your HLS stream includes a well-structured bitrate ladder—a range of bitrate options that allows the player to transition seamlessly between quality levels based on network conditions.

You can check the available bitrates and manually set a preferred bitrate range:

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Swift

1if let asset = player.currentItem?.asset as? AVURLAsset { 
2    let preferredBitrate = 800_000  // Set in bps 
3    asset.resourceLoader.setPreloadsEligibleContentKeys = true 
4    player.currentItem?.preferredPeakBitRate = Double(preferredBitrate) 
5} 

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Setting a bitrate limit can prevent sudden drops to low-quality streams, especially on unstable networks.

With FastPix video API,  you automatically optimizes bitrate ladders, ensuring consistent quality transitions and a frustration-free streaming experience for your viewers.

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6. Handle audio/video sync issues

In HLS streaming, out-of-sync audio and video can significantly impact the viewing experience. This desynchronization typically results from mismatched segment durations, codec inconsistencies, or issues with encoding settings. Here’s how to address and prevent these issues, ensuring that audio and video stay in sync throughout playback. If you encounter persistent sync issues, consider adjusting AVPlayer settings:

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Swift

1player.automaticallyWaitsToMinimizeStalling = false 

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This can reduce instances of out-of-sync playback by allowing the player to adjust timing without waiting.

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Firewall and ports

Sometimes, a firewall can cause problems with streaming. This can occur both with the firewall on your own computer, or firewalls that are integrated into the network itself.

1. Port requirements and HTTP/S protocol access

• HLS live streaming typically transmits data over HTTP (port 80) or HTTPS (port 443). It’s crucial to verify that both ports are open for inbound and outbound traffic, as these are essential for the retrieval of .m3u8 playlist files and .ts media segments.
• Any firewall blocking port 80 or 443 on the client or server network will disrupt stream initiation and playback. Ensure TCP traffic on these ports is unrestricted to allow seamless HLS delivery across different network environments.

2. Deep packet inspection and data filtering

• Firewalls with deep packet inspection (DPI) can interfere with HLS traffic by examining or filtering HTTP/S requests based on packet size or content type. This can result in slower response times or blocked media segments.
• To maintain efficient HLS performance, configure the firewall to allow unfiltered access to HLS data packets or establish bypass rules for known streaming domains, including CDN addresses that distribute .m3u8 and .ts files.

3. NAT Traversal and session persistence

• For networks employing NAT (Network Address Translation), session persistence (or "sticky sessions") is critical to maintaining continuous HLS playback. NAT devices should be configured to handle persistent TCP sessions for streaming traffic to prevent session drops that cause buffering and re-buffering issues.
• HLS segments are typically delivered in a continuous sequence; NAT routers must retain consistent port mappings for each client’s stream to avoid broken connections during playback.

4. CDN and IP allowlisting

• Content delivery networks (CDNs) are often used to cache and deliver HLS content. Many CDNs serve HLS streams across a range of IP addresses or dynamically load-balance traffic across several points of presence (PoPs). Firewalls should be configured to allow all IP ranges associated with the CDN to prevent access denial to media segments.
• In cases where IP allowlisting is enforced, verify the IP ranges for the CDN in use (e.g., Akamai, Cloudflare) and add them to the firewall's allowlist to ensure uninterrupted access to all HLS components.

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Advanced debugging techniques for iOS

For iOS developers, identifying the root cause of HLS streaming issues can sometimes require going beyond standard troubleshooting methods. Advanced debugging techniques allow for deeper insights into how your app interacts with HLS streams and where potential playback issues may lie. These methods leverage internal diagnostics and network monitoring to gain more granular data about playback performance, network conditions, and user experience.

In this section, we’ll explore two techniques: enabling AVFoundation logging and using quality of experience (QoE) metrics. By activating AVFoundation's detailed logging, you can capture comprehensive information about asset loading, playback errors, and network status changes directly from AVPlayer. Meanwhile, implementing QoE metrics helps track key performance indicators like rebuffering frequency, average bitrate, and startup latency, which are essential for understanding the end-user experience.

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1. Enable AVFoundation Logging

When troubleshooting playback issues in your HLS stream, one of the most effective ways to gain deeper insights is by enabling detailed logging in AVFoundation. This powerful logging feature captures valuable data about how AVPlayer handles asset loading, network conditions, and errors, giving you a clearer view of what might be affecting stream performance.

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Swift

1UserDefaults.standard.set(true, forKey: "AVFoundationLogging") 

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Logs will output to the console, allowing you to trace exactly where playback might be failing.

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2. Use Quality of experience (QoE) Metrics

If you’re implementing custom analytics, consider using QoE metrics like rebuffering rate, average bitrate, and startup time. Tracking these metrics can help identify patterns in user experiences and optimize your stream delivery accordingly.

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Final Thoughts

Wrapping up, troubleshooting HLS live streams doesn’t have to be a headache. With the right steps, you can turn streaming issues into opportunities to improve the experience, ensuring your viewers stay engaged and enjoy your content without interruptions.

At FastPix, we make streaming simpler. Whether you’re working with HLS or other formats, our platform ensures smooth video delivery and top-notch performance. Our multi-CDN technology guarantees fast, reliable streams across various protocols, so your audience can focus on your content, not the loading screen.