MacOS: Customizing Video Cue Background With HLS.js

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Customizing Video Cue Background Color with HLS.js on macOS

Are you struggling to customize the background color of video cues when using hls.js on macOS? You're not alone! Many developers have encountered issues trying to modify the default black background of text tracks to make them transparent on macOS, specifically in browsers like Safari, Chrome, and Edge. This article dives into the problem, explores potential solutions, and provides a detailed guide to help you achieve the desired transparent background for your video cues.

The Problem: Inconsistent Behavior Across Platforms

The primary issue is the inconsistent behavior of the video::cue CSS selector across different operating systems. While setting background-color to transparent or rgba(0,0,0,0) works perfectly fine on Windows, it often fails to produce the same result on macOS. This discrepancy can be frustrating, especially when you're aiming for a consistent user experience across all platforms. The default black background stubbornly persists, making it difficult to integrate the subtitles seamlessly with the video content.

Why Does This Happen?

The exact reasons for this behavior are complex and can be attributed to differences in how various browsers and operating systems render video cues. macOS, in particular, seems to have specific rendering engines that handle video cues differently than their Windows counterparts. This can lead to unexpected CSS behaviors and make it challenging to override default styles.

Understanding the Code: A Detailed Look

Let's break down the code snippet you provided and understand how each part contributes to the video playback and subtitle rendering process. This will help us identify potential areas for modification and customization.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>Custom background Vide Cue</title>
    <script src="https://cdn.jsdelivr.net/npm/hls.js@latest"></script>

    <style>
      video::cue {
        background-color: rgba(0, 0, 0, 0);
        background-color: transparent;
      }
    </style>
  </head>
  <body>
    <h2>HLS.js Simple Example</h2>
    <video
      id="video"
      width="640"
      height="360"
      muted
      autoplay
      playsinline
    ></video>

    <div>
      <button id="prev10">âȘ Prev 10s</button>
      <button id="next10">⏩ Next 10s</button>
    </div>

    <!-- Load HLS.js from CDN -->
    <script>
      const video = document.getElementById("video");
      const hlsUrl =
        "https://vodcdn.fptplay.net/POVOD/encoded/2025/06/14/thefirstnightwiththeduke-2025-kr-001-v4-ea995d6e9c86786a/H264/master.m3u8"; // sample HLS stream

      if (Hls.isSupported()) {
        const hls = new Hls();
        hls.loadSource(hlsUrl);
        hls.attachMedia(video);

        hls.on(Hls.Events.MANIFEST_PARSED, () => {
          console.log("HLS manifest loaded");
          video.play();
        });

        hls.on(Hls.Events.SUBTITLE_TRACKS_UPDATED, (_, data) => {
          const tracks = data.subtitleTracks;
          console.log("Subtitle tracks:", tracks);

          if (tracks.length > 0) {
            // Find default or first available subtitle track
            const defaultIndex = tracks.findIndex((t) => t.default);
            const firstIndex = defaultIndex !== -1 ? defaultIndex : 0;

            hls.subtitleTrack = firstIndex;
            console.log(
              `Default subtitle track set: ${
                tracks[firstIndex].name || tracks[firstIndex].lang
              }`
            );
          } else {
            console.log("No subtitle tracks found");
          }
        });
      } else if (video.canPlayType("application/vnd.apple.mpegurl")) {
        // For Safari (it supports HLS natively)
        video.src = hlsUrl;
        video.addEventListener("loadedmetadata", () => video.play());
      } else {
        alert("Your browser does not support HLS playback.");
      }

      // Skip buttons
      document.getElementById("next10").addEventListener("click", () => {
        video.currentTime = Math.min(video.currentTime + 10, video.duration);
      });

      document.getElementById("prev10").addEventListener("click", () => {
        video.currentTime = Math.max(video.currentTime - 10, 0);
      });
    </script>
  </body>
</html>

Key Components

  • HLS.js Library: This library enables HLS (HTTP Live Streaming) playback in browsers that don't natively support it. It's crucial for delivering adaptive bitrate streaming.
  • Video Element: The <video> element is the container for the video content. Attributes like id, width, height, muted, autoplay, and playsinline control its behavior.
  • CSS Styling: The <style> section attempts to modify the background color of video cues using the video::cue selector.
  • JavaScript Logic: This part of the code initializes HLS.js, loads the HLS stream, attaches it to the video element, and handles subtitle track selection. It also sets up event listeners for skipping forward and backward in the video.

Potential Solutions and Workarounds

While directly setting background-color: transparent on video::cue might not work on macOS, here are several alternative approaches you can try:

1. Using ::cue-region (Experimental)

Some newer browsers support the ::cue-region pseudo-element, which allows you to style the region behind the text. This might offer more control over the background. However, be aware that this is still an experimental feature and may not be supported in all browsers.

video::cue-region {
  background-color: transparent !important;
}

2. JavaScript-Based Styling

Instead of relying solely on CSS, you can use JavaScript to dynamically modify the styles of the video cues. This involves accessing the active text tracks and manipulating their styles directly.

video.textTracks[0].addEventListener('cuechange', function() {
  var cues = this.activeCues;
  for (var i = 0; i < cues.length; i++) {
    cues[i].style.backgroundColor = 'transparent';
  }
});

Note: You might need to adapt the index 0 to the correct text track index.

3. WebVTT Styling

If you have control over the WebVTT (Web Video Text Tracks) files, you can embed styling information directly within the VTT file itself. This can sometimes override the default styles more reliably.

WEBVTT

STYLE
::cue {
  background-color: transparent;
}

00:00:00.000 --> 00:00:05.000
This is a subtitle with a transparent background.

4. Shadow DOM Manipulation (Advanced)

Some advanced techniques involve accessing the shadow DOM of the video element and manipulating the styles directly within the shadow DOM. This is a more complex approach but can provide a greater degree of control over the rendering of video cues. You can inspect the shadow DOM in your browser's developer tools to understand its structure.

5. Browser-Specific Hacks (Use with Caution)

As a last resort, you might consider using browser-specific CSS hacks to target macOS browsers specifically. However, this approach is generally discouraged because it can lead to brittle code that breaks when browsers are updated.

@media screen and (-webkit-min-device-pixel-ratio:0) { /* Safari and Chrome on macOS */
  video::cue {
    background-color: transparent !important;
  }
}

Debugging and Troubleshooting

  • Inspect Element: Use your browser's developer tools to inspect the video::cue element and see which styles are being applied. Pay attention to any conflicting styles that might be overriding your background-color setting.
  • Console Logging: Add console.log statements to your JavaScript code to verify that the text tracks are being accessed correctly and that the styles are being applied.
  • Browser Compatibility: Test your code in different browsers on macOS to see if the issue is specific to a particular browser.
  • Simplify: Start with a minimal example to isolate the problem. Remove any unnecessary code to make it easier to identify the source of the issue.

Alternative Approaches

  • HLS.js Configuration: Explore HLS.js configuration options. There might be settings that influence how subtitles are rendered.
  • Custom Subtitle Rendering: As a more advanced approach, consider implementing your own subtitle rendering logic using JavaScript and HTML. This gives you complete control over the appearance of the subtitles but requires more development effort.

Conclusion: Persistence is Key

Customizing the background color of video cues on macOS with hls.js can be challenging due to inconsistencies in browser rendering. By trying different approaches, such as using ::cue-region, JavaScript-based styling, or WebVTT styling, you can often find a solution that works for your specific use case. Remember to debug thoroughly and test your code across different browsers to ensure a consistent user experience. Don't be afraid to experiment and adapt your approach until you achieve the desired result. Good luck, guys!