Videos you shot years ago on an older smartphone, a digital camera, or a flip phone look blurry on today’s iPhone or TV, and blocky compression noise stands out. That’s because footage recorded at 640×480 or 1280×720 is being stretched to fill a much larger screen.
ReMaster is an iPhone and iPad app that uses AI to upscale videos and photos like these by up to 4× and turn choppy 30fps motion into smooth 60fps. This article explains how to use it, what happens inside the app, and why it can be offered without a subscription.
How much sharper does it actually get?
First, take a look at the results. We shrank a photo to 640×360 pixels (about the size of old cell phone video) and compressed it as a JPEG to create a “frame from an old video.” We then enlarged it 4× to 2560×1440 and cropped a section.
The left side was simply enlarged using the same method as many video players and editing apps (Lanczos resampling). The right side was enlarged with ReMaster’s AI Super Resolution, using the same AI model and the same processing code as the app, with the default settings.
A simple enlargement can’t create information that isn’t in the original, so edges bleed and the whole image looks soft. With AI Super Resolution, the letters on the keys and the outlines of the envelope and phone icons become crisp, and you can even make out the corners of the blocks and the wood grain. Compression noise also becomes much less noticeable.
This is done for every single frame of a video.
How to use it
1. Choose a video
On the first screen, choose a video or photo.
- Choose from Photos: Pick videos and photos directly from the Photos app. Select several to process them together
- Choose from Files…: Choose a video stored in the Files app
- Process a Folder…: Process all the videos and photos in a folder, one after another
Supported formats are MOV / MP4 / M4V for video and JPEG / PNG for photos. HEIC photos from the Photos app are automatically converted to JPEG when imported.
2. Choose your export settings
After you choose a video, the Export Settings screen appears.
- Upscaling Method: Choose “AI Super Resolution” or “Standard (Lanczos).” AI Super Resolution delivers higher quality but takes longer, because the AI processes every frame one by one. Choose Standard when you’re in a hurry
- Resolution: Choose from “Original size (quality only),” HD, Full HD, WQHD, 4K, and ×2 to ×4. Only sizes larger than the original video are listed, and the size one step above the original is selected by default
- Frame Rate: Choose “Unchanged,” “×2 (Smoother),” or “Convert to 60 fps”
- Detail Enhancement: Adjusts how crisp the edges become. The default is 15% for AI Super Resolution and 50% for Standard
- Save: Choose the format (MP4 / MOV, or JPEG / PNG for photos), the file name, and where to save (Photo Library / Files)
3. Export
Tap Export to start processing; progress is shown as a percentage. The screen won’t auto-lock while processing, so keep the app open until it finishes.
When it’s done, you’ll see “Export complete,” and you can view the result in the Photos app or share it.
4. Process several files at once
If you select several videos in the Photos app, or choose a folder with “Process a Folder…,” ReMaster exports them one by one with the same settings.
You set the size either as a scale factor, such as “×2,” or by the length of the long side, such as “Full HD (long side 1920).” If a file fails partway through, processing keeps going, and you can review the results in a list at the end.
How it works: what happens inside the app
AI Super Resolution (Real-ESRGAN)
To improve image quality, ReMaster uses the open-source Real-ESRGAN model (realesr-general-x4v3).
Real-ESRGAN is a model trained on pairs of images: a clean image and a copy deliberately degraded by blurring, adding noise, and compressing it. Because it has learned to “estimate the original clean image from a degraded one,” feeding it a frame from an old video returns an image four times larger, with edges and textures filled in.
ReMaster splits each frame into 512×512-pixel tiles, runs them through the AI to enlarge them 4×, and then puts them back together. Neighboring tiles are processed with a 32-pixel overlap and joined in the middle of each overlap, so no seams appear. To reach the size you chose, the 4× image is then scaled down to fit. For example, with “×2,” the frame is enlarged 4× and then halved.
This is done for every frame in the video. A 30fps video has 1,800 frames per minute, which is why AI Super Resolution takes time.
Keep in mind that the AI doesn’t bring back things that were never captured. It estimates and paints in “plausible details” based on what it has learned. Very fine details that cover only a few pixels in the original, such as a distant cityscape, can end up looking like a painting. If that bothers you, lower Detail Enhancement or compare the result with Standard (Lanczos).
Frame interpolation (RIFE)
Motion smoothing is handled by RIFE (v4.25), which is also open source. From two consecutive frames, it estimates “what moved in which direction” and generates brand-new frames in between.
- ×2 (Smoother): Adds one new frame between every pair of frames. 30fps becomes 60fps, and 60fps becomes 120fps
- Convert to 60 fps: Creates a frame for every 1/60 of a second, so you can turn 24fps or 30fps video into 60fps
Interpolation is done at the original resolution, and the generated frames also go through AI Super Resolution. Converting to 60fps doubles the number of frames, so processing takes longer too.
Reading and writing video
ReMaster uses the video features built into iOS to read and export video. Exported video is compressed with HEVC (H.265) when the long side exceeds 1920 pixels, and with H.264 otherwise. If the original audio is AAC, it’s kept as is; otherwise it’s converted to AAC.
Everything runs on your iPhone
Both AI models have been converted to Apple’s Core ML format and built into the app. Processing runs on the Neural Engine and GPU of your iPhone or iPad, and your videos are never sent anywhere. The app connects to the network only to verify purchases with the App Store, and no account is required.
Why it’s not a subscription
Most AI video enhancement services upload your video to a server and process it on cloud GPUs. GPU servers are expensive, and the cost grows with the length of the video being processed. That’s why these services tend to charge a monthly fee or use credits based on processing time. The longer the video, the more you pay, and the longer the upload takes.
ReMaster does away with this model by running open-source AI models right on your iPhone.
- No server costs: Real-ESRGAN is released under the BSD 3-Clause license and RIFE under the MIT license, both of which allow them to be built into apps. Because all processing happens on your own iPhone, we don’t pay server costs for each video
- So it’s free to use: Every feature, including AI Super Resolution, 60fps conversion, and batch processing, is free. The only limitation is a watermark (the app icon) on exported videos. Photos never get a watermark
- Removing the watermark is a one-time purchase: Buy “ReMaster Premium” once to export without the watermark. There’s no monthly fee
- Your videos never leave your device: You can process private videos, like family footage, with peace of mind. There’s no waiting for uploads and no size limit, either
The trade-off is that processing speed depends on the performance of your iPhone or iPad. Upscaling a long video to 4K takes a while, so we recommend keeping your device plugged in while it works.
We’re grateful to the developers who made the Real-ESRGAN (Xintao Wang et al.) and RIFE (hzwer et al.) models publicly available. You can read the full license texts under “Open Source Licenses” on the app’s first screen.
Tips for the best results
- Low-resolution videos benefit the most: Videos at 640×480 or 1280×720 can look dramatically better. Videos at Full HD or above are already sharp, so the change is more subtle
- Try a short clip first: Settle on your settings before moving on to long videos or batch processing, so you don’t waste time
- Use 60fps for videos with lots of motion: Videos of school sports days and other sports look smoother with “Convert to 60 fps.” In videos with frequent scene changes, the frames right before and after a cut may look unnatural. If that happens, compare the result with “Unchanged”
- In a hurry? Use Standard (Lanczos): It enlarges without AI, so it finishes quickly
- Exported videos are saved as new files: The original capture date isn’t carried over, so in the Photos app they appear under the date you exported them
Summary
- ReMaster is an app that enhances old videos and photos by running AI super resolution (Real-ESRGAN) and frame interpolation (RIFE) on your iPhone or iPad
- Because the open-source models run on your device, there are no server costs and the app is free to use. Premium, which removes the watermark, is a one-time purchase
- Your videos are never uploaded, and no account is required
- Available for iPhone and iPad running iOS 26 or later