Does compressing video lose quality on iPhone?

The short answer

Yes, compressing video loses some detail. A compressor has to throw information away to make the file smaller, and it cannot put that information back. But on an iPhone, the loss is often hard to see. Emptie turned a 5-minute 4K Dolby Vision video into a 1080p HEVC file at 8 megabits per second. It went from 2.18 GB to 323 MB, with no visible loss on the phone. You can still see a difference when you zoom in, crop, or view on a large screen, so check the result on the footage that matters to you.

What “lossy” means

A lossless file decodes to exactly the frames it started from. A lossy file does not. HEVC, the codec Emptie writes, is a lossy codec. It discards detail that it estimates the eye is least likely to notice, which is why the file gets smaller.

Loss adds up when you re-encode a file again and again. Each pass throws away a little more. The safer habit is to compress once, from the original, and keep the original until you have checked the result. Emptie works this way: each video is compressed from its Original, and the Original stays in the library until you confirm the Compressed Copy.

Why the loss is often invisible on a phone

Four things work together.

HEVC is efficient. The HEVC standard is designed to reach the same quality as H.264 at a lower bitrate. Wikipedia’s summary of HEVC says it can achieve “from 25% to 50% better data compression at the same level of video quality” than AVC, the standard behind H.264. A Compressed Copy in HEVC can therefore be much smaller without a large step down in quality.

The bitrate sets the detail. The bitrate is how many bits each second of video gets. Emptie’s example above used 8 megabits per second for 1080p. The third-party figures in our storage guide put 1080p at 30 fps in HEVC at about 60 MB per minute, which works out to the same 8 megabits per second. That is the rate at which the example showed no visible loss. It is one clip, so it is not a rule for every video.

The screen has a fixed number of pixels. The iPhone 14 Pro has a 6.1-inch display with 2556 by 1179 pixels at 460 ppi, according to Apple’s iPhone 14 Pro tech specifications. Viewed in landscape, that is 2556 pixels across.

• A 4K frame is 3840 pixels across. On a 2556-pixel screen, each screen pixel shows about 1.5 video pixels, so the phone already shows less than the full 4K detail when the whole frame is on screen.
• A 1080p frame is 1920 pixels across. Each video pixel is stretched over about 1.33 screen pixels.

So the detail a 1080p copy drops from a 4K original is detail the phone cannot show at full frame. The loss becomes visible when you zoom in, crop, or play the video on a TV or computer, where the 4K original has more to show.

Fast motion and dark scenes are the usual test. Lossy encoders tend to show their work first in fine texture, fast movement and shadows. Those are the places to look when you compare an original with a compressed copy.

What Emptie keeps

Emptie does not change the things that matter most for how a video looks and sounds, except the size of the file.

• Frame rate. Presets keep the Original’s frame rate, so a 60 fps video stays at 60 fps. At the same bitrate, a 30 fps copy came out at 325 MB, against 323 MB for the 60 fps copy, and it looked less smooth. Lowering the frame rate barely saves space, so it is a separate choice under Advanced Settings.
• HDR and Dolby Vision. Emptie is designed to keep HDR and Dolby Vision in the Compressed Copy. Apple’s iPhone 14 Pro specifications list HDR recording with Dolby Vision up to 4K at 60 fps, which is the top setting on that model.
• Sound. The sound track is copied over unchanged.
• The details of the library item. The date recorded, location, Favorite, Hidden and membership in your own albums carry over to the Compressed Copy.

Emptie writes every Compressed Copy as HEVC. It also leaves a video alone when the Compressed Copy would save less than about 20%, because a small saving is not worth a new encode.

The size and the visible loss are set by the Preset you choose. The three Presets are High Quality, Balanced and Max Savings. Balanced is the default. Each one fixes a Resolution and a Compression Level, and a higher Compression Level gives a smaller file with more visible loss. High Quality keeps the most detail at the largest size, and Max Savings gives the smallest file and the most loss. If you want to control the Resolution and Compression Level yourself, Advanced Settings lets you choose them directly. Whichever you pick, the Review step shows you the result before anything is replaced.

When not to compress

Most everyday clips are good candidates. The cases below are not.

• Footage you will edit or grade. If a video is the source for a professional edit or colour grade, keep the original. Every extra encode adds loss that cannot be undone. For scale, Apple’s ProRes page says “ProRes files are up to 30 times larger than HEVC files.”
• Cinematic, Slo-mo and Spatial video. Emptie does not compress these, because doing so would remove their special features. They appear in the library with a “Not supported yet” label. Apple’s tech specifications list Cinematic mode up to 4K HDR at 30 fps and slow motion at 1080p up to 240 fps.
• Video you have already compressed. A file that has been through several encodes has less detail to lose, and another pass will save little.
• Video you need at full detail for a big screen. If you plan to show a clip on a large display or crop it heavily, check the Compressed Copy at that size first.
• Clips you cannot shoot again. A first-birthday clip or a one-off recording is worth a slower, more careful check than a screen recording you could repeat. Use High Quality for those, and review both versions at full size before you confirm.

Check before anything is deleted

Emptie isn’t out yet; this is its Review step as designed. Emptie does not delete an Original when a Batch finishes. It shows each one next to its Compressed Copy:

1. Side-by-side playback. Review plays the Original and the Compressed Copy side by side, with the size of each shown before and after.
2. Keep original. Each video has its own toggle. Turn it on to keep the Original, and that video is not replaced.
3. Checks before the library changes. Each Compressed Copy must play and match the Original’s duration. If a check fails, that video keeps its Original.
4. One confirmation. The Replace button names the number of videos, and iOS asks you once for the whole group. Nothing is deleted before you tap it and confirm.
5. Recently Deleted. The Originals go to Recently Deleted. Apple’s Recently Deleted page says “When you delete photos and videos, they go to your Recently Deleted album for 30 days.” You can recover them until then.

A simple test before you start a large Batch: compress one video, then play both at full screen. Pause on a fast scene and a dark scene, zoom in on a face or a sign, and check how the copy looks on a TV or a computer if you watch videos there. The test covers the cases where loss usually shows first, so it is a fair check. It is not a guarantee for every video, which is why Review compares each one.

For the storage side of the same question, see how much storage iPhone video takes. For the steps to compress one video by hand, see how to compress video on iPhone. If you are comparing apps, see the best video compressor for iPhone page.

Frequently asked questions

Does compressing a video lower its quality?

It can. Re-encoding is lossy, so the new file keeps less detail than the original. Whether you can see the difference depends on the bitrate, the screen and what you look at. One 5-minute 4K video compressed to 1080p HEVC by Emptie shows no visible loss on the phone.

Can you compress video on iPhone without losing quality?

Not strictly. The only lossless option is keeping the original file. Compressing with HEVC at a sensible bitrate can make a file much smaller while the difference stays hard to see, but it is still a new, lossy encode.

Does HEVC look worse than H.264?

Not by design. HEVC is built to reach the same quality at a lower bitrate than H.264, and Wikipedia’s summary reports 25% to 50% better compression at the same quality. Results still depend on the encoder settings, so compare the two on your own footage.

Will Emptie keep HDR and Dolby Vision?

Emptie is designed to keep HDR and Dolby Vision in the Compressed Copy, and to copy the sound unchanged. The Compressed Copy is always HEVC. You can compare each one in Review before anything is replaced.