Hey there, let’s break down your questions step by step—this is a super common pain point when hunting for budget GPU acceleration for video tasks, so I’ll try to make this clear and actionable.

1. Avidemux硬件加速的那些小细节 #

First, let’s untangle the confusion you’re seeing with your current cards:

• NVIDIA CUDA & H.264 support: Avidemux can often detect basic H.264 hardware encoding on NVIDIA GPUs without CUDA Toolkit installed—this is because many older NVIDIA cards have a dedicated NVENC chip built-in for basic encoding. Installing CUDA Toolkit usually unlocks more advanced CUDA-powered processing (like custom filtering paired with encoding), but the core hard encoding works out of the box.
• AMD VCE/VCN missing from list: Avidemux’s support for AMD’s video encoding tech (VCE/VCN) can be finicky. For your K420, the issue is simple: it’s a professional graphics card built for CAD/3D modeling, not video work—it has almost no dedicated video encoding hardware, even if it supports OpenCL (OpenCL is for general-purpose computing, not specialized video encoding). As for your friend’s 6600XT, that’s likely an Avidemux version problem—older builds don’t support newer AMD cards well, so updating to the latest stable release should fix that.
• Intel UHD 630: This has Intel’s QSV (Quick Sync Video) encoding built-in, which Avidemux should support for basic H.264/H.265 encoding. It’s not blazingly fast, but it works for 1080p tasks.

2. The only GPU parameters that matter for video encoding #

You can ignore most of the specs you see on comparison sites—here’s what actually counts:

• Dedicated video encoding hardware: This is non-negotiable. Look for terms like NVENC (NVIDIA), VCE/VCN (AMD), or QSV (Intel). These are specialized chips on the GPU that handle video encoding independently—floating point performance, texture fill rate, etc., are for gaming/rendering and don’t affect video encoding speed at all.
• Encoding format support: Make sure the card supports the formats you use (H.264 is standard, but H.265/HEVC is better for smaller files). Also check resolution/frame rate limits if you work with 4K or high-fps footage.
• Software compatibility: Even if the card has the hardware, Avidemux needs to support its API. Always cross-check the Avidemux docs for supported GPUs before buying.

3. Your budget GPU option: RX580 #

The RX580 is a great pick for your needs:

• It has a dedicated VCE 3.0 encoding unit that handles H.264 and H.265 with solid speed, way faster than your UHD 630.
• As long as you install the latest AMD Adrenalin drivers and use the newest Avidemux version, it should show up in the hardware acceleration list without issues.
• Used RX580s are cheap and widely available, making them perfect for budget video tasks like cropping and encoding.

Quick final tips #

• Update Avidemux to the latest stable release first—this fixes most hardware detection bugs.
• Avoid professional graphics cards (like the K420) for video work; they’re optimized for 3D/CAD, not encoding.
• When buying used, double-check that the card explicitly lists support for VCE/VCN (AMD) or NVENC (NVIDIA) in its specs.

备注：内容来源于stack exchange，提问作者Gyula Molnár