Microsoft Silverlight (64-bit) for Windows

Microsoft Silverlight (64-bit) is a free browser plug-in runtime once used to power rich media and apps on the web. It focuses on playback mechanics such as Smooth Streaming for adaptive video and PlayReady DRM for protected content, helping sites deliver consistent performance under changing networks while keeping licensing intact for premium streams.

Beyond video, Microsoft Silverlight (64-bit) supports interactive content through Deep Zoom image navigation and a developer model built on XAML UI, so experiences can respond to input and data in real time. Today, it is relevant mainly for specific legacy sites that still depend on its engine and packaging.

Capabilities, limitations, and smart alternatives

Under the hood, apps use SmoothStreamingMediaElement to manage adaptive playback while responding to events from the stream manifest. Built-in closed captions support and playlist support simplify long-form programming, and manifest-based control lets developers track quality shifts and errors cleanly. In practice, the runtime delivers steady performance under variable bandwidth, reducing stalls and keeping audio and video in sync across segments and bitrate switches. Latency stays predictable during scrubs and seeks.

Usability varies with the environment. Because it relies on a browser plug-in, compatibility hinges on legacy support that many modern setups restrict, which raises maintenance overhead. On the plus side, adaptive delivery and rights management work reliably for long sessions. On the minus side, limited compatibility and no ongoing updates make it a risky dependency for new deployments, and troubleshooting can require specialized knowledge that teams may no longer retain.

For teams maintaining older sites, the runtime remains serviceable when a compatible browser is guaranteed. For fresh projects, adopt HTML5 players using DASH or HLS pipelines with MSE and EME for content protection, which significantly reduces plugin friction and future-proof delivery. In short, pros include dependable streaming and solid protection; cons include aging dependencies, shrinking browser support, and reduced long-term maintainability relative to modern stacks.

Useful only for strict legacy needs

Microsoft Silverlight (64-bit) delivers proven adaptive streaming and content protection for sites built around its runtime, but it belongs in maintenance mode. It is recommended only when a legacy workflow requires it and a compatible browser is guaranteed. New builds should favor standards-based DASH or HLS on HTML5 players to reduce operational risk while keeping performance and protection goals intact, and to align teams with mainstream, well-supported tooling.

• Version 5.1.50907.0 include security hardening: addresses a remote code execution risk in Silverlight that could be triggered by a specially crafted Silverlight app loaded from a compromised site
• Patch identifier: aligns with Microsoft’s KB4023307 security update for Silverlight 5
• Scope of change: security-only; no new user-visible features were introduced