How do you use this tool?
- Click or drag your HEVC/H.265 video file into the drop zone (.mov, .mp4, .hevc).
- Adjust output settings if needed: quality (CRF), resolution, or audio codec.
- Click Convert — the browser encodes the file locally using WebAssembly.
- Download the finished H.264 MP4 file when the progress bar completes.
What This Tool Does
This tool converts HEVC (H.265) video files to H.264 MP4 — entirely in your browser. It uses FFmpeg compiled to WebAssembly (WASM), which means the encoding runs on your CPU locally, just like a native app, but without requiring any installation. Supported input formats include .mov, .mp4, and .hevc containers carrying H.265 video streams. The output is a standard H.264 MP4 that plays on virtually any device, platform, or video host.
How Does It Work?
The conversion pipeline inside the browser looks like this:
Input file (HEVC/H.265 stream)
↓
Demux: extract raw video + audio streams
↓
Decode: HEVC decoder (software) → raw YUV frames
↓
Encode: H.264 encoder (libx264 via FFmpeg WASM) → compressed H.264 stream
↓
Mux: wrap in MP4 container
↓
Output: .mp4 (H.264 video + AAC audio)Key Encoding Parameters
| Parameter | Default | What It Controls |
|---|---|---|
| CRF (Constant Rate Factor) | 22 | Quality vs. file size. Lower = better quality, larger file. Range: 0–51 |
| Preset | medium | Speed vs. compression efficiency trade-off |
| Audio codec | AAC 128 kbps | Broad compatibility |
| Resolution | Source | Can be scaled down (e.g., 4K → 1080p) |
# Equivalent FFmpeg command (runs inside the browser via WASM):
ffmpeg -i input.mov -c:v libx264 -crf 22 -preset medium -c:a aac -b:a 128k output.mp4Codec Comparison
| Property | H.264 (AVC) | HEVC (H.265) |
|---|---|---|
| Compression efficiency | Baseline | ~50% better |
| Browser support | Universal | Partial (Safari, Edge) |
| Hardware decode | Universal | Newer devices only |
| File size at same quality | Larger | Smaller |
| Encoding speed | Fast | Slower |
What Are Common Use Cases?
Sharing iPhone videos with Windows users. iPhones record in HEVC by default since iOS 11. When an iPhone user sends a .mov file to a Windows user who hasn’t installed the HEVC codec pack, they get an error. Converting to H.264 MP4 solves this without any setup on the recipient’s end.
Uploading to video platforms and social media. Most platforms accept H.264 natively and re-encode to their own formats. While some (YouTube, Vimeo) also accept H.265, others — older social platforms, corporate video portals, learning management systems — still only handle H.264. Converting first ensures the upload succeeds and avoids unexpected transcoding artifacts.
Editing in older or budget software. Adobe Premiere Pro and DaVinci Resolve handle HEVC, but older versions, low-end video editors, and lightweight screen recording apps often don’t. Converting to H.264 makes footage editable in virtually any video software released in the last 15 years.
Embedding video on websites. The HTML5 <video> element supports H.264 universally across all major browsers. HEVC browser support is inconsistent — it works in Safari and Edge but not in Firefox. H.264 is the safe choice for web embeds.
Archiving drone footage for broad access. Consumer drones (DJI, Autel) offer HEVC recording for more efficient storage. If you’re sharing footage with clients or colleagues who may view it on any device, H.264 ensures no compatibility issues.
Frequently Asked Questions
What is HEVC / H.265?
HEVC stands for High Efficiency Video Coding. Standardized in 2013 and sometimes called H.265, it’s the successor to H.264 (AVC). It delivers roughly the same visual quality as H.264 at about half the bit rate — or equivalent quality in half the file size. Apple adopted HEVC as the default iPhone recording codec in iOS 11 (fall 2017) and macOS High Sierra.
Why doesn’t my H.265 video play on Windows?
Windows 10 and 11 can play HEVC files, but only if you have the correct codec installed. Microsoft distributes the HEVC Video Extensions as a paid add-on from the Microsoft Store ($0.99). Many users don’t have it. Additionally, older versions of Windows (7, 8.1) have no HEVC support at all. Converting to H.264 eliminates this dependency entirely.
Will the video quality be worse after conversion?
Yes, slightly — this is called generation loss, and it’s unavoidable when re-encoding video. Every encode introduces minor artifacts because you’re compressing an already-compressed signal. However, at a CRF value of 18–22 in libx264, the quality difference compared to the HEVC source is imperceptible for most content on most screens. For archival purposes, keep your original HEVC file and only distribute the H.264 version.
How large can the input file be?
This depends on your browser and device RAM. Modern Chromium-based browsers (Chrome, Edge) and Firefox typically handle files up to 2 GB comfortably. Files in the 2–4 GB range work on most desktop systems with 8+ GB of RAM. Files larger than 4 GB may cause issues — for those, split the video into segments first using a tool like VLC or FFmpeg natively installed.
Is my video uploaded to any server?
No. The conversion runs entirely within your browser using FFmpeg compiled to WebAssembly. The WASM binary downloads once when you first load the tool, but your video file is processed entirely in local memory. No upload occurs. You can confirm this by monitoring network activity in browser DevTools — no outbound file transfer will appear during conversion.
How long does conversion take?
Software H.264 encoding (libx264) is CPU-intensive. Rough benchmarks on a modern laptop (M1 MacBook Air or recent Intel/AMD):
- 1-minute 1080p clip: 1–3 minutes
- 5-minute 1080p clip: 5–15 minutes
- 4K footage: 3–5× longer than 1080p
Encoding speed scales with CPU speed and core count. The browser may use multiple threads via SharedArrayBuffer if your environment supports it. Closing other browser tabs and apps speeds things up on memory-constrained systems.
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