How HEVC Technology Revolutionizes Mobile Video Compression

Every time you record a video on your iPhone, a piece of silicon the size of a fingernail performs billions of calculations per second to compress 8.3 million pixels per frame into a file small enough to store on your phone. The algorithm driving this process is HEVC—High Efficiency Video Coding—and it's the reason you can carry thousands of videos in your pocket.

HEVC (also called H.265) doesn't just compress video a little better than its predecessor H.264. It compresses roughly twice as efficiently, meaning the same quality video in half the file size. This single technology advancement has saved iPhone users billions of dollars in storage costs and enabled 4K recording to become standard on mobile devices.

But how does it actually work? And why is it so much better than H.264? Understanding the technology helps you make better decisions about recording settings, compression, and storage management.

The Core Problem: Redundancy

Video compression works by finding and eliminating redundancy. A raw 4K video at 30fps produces 12 GB per minute because it stores every pixel of every frame independently. But most of that data is redundant:

Spatial redundancy: Within a single frame, nearby pixels tend to look similar. A blue sky has millions of pixels that are nearly identical. Instead of storing each one, the codec describes the pattern once and references it.

Temporal redundancy: Between consecutive frames, most of the image doesn't change. If a person is standing in a room, 90% of the frame might be identical to the previous one. The codec only needs to encode what changed.

Statistical redundancy: Some pixel values and patterns occur far more frequently than others. Variable-length encoding assigns shorter codes to common values and longer codes to rare ones.

H.264 already exploits all three types of redundancy. HEVC does the same thing—but with dramatically more sophisticated tools at every stage.

Innovation 1: Flexible Block Partitioning

Both H.264 and HEVC divide each frame into rectangular blocks and process them individually. The key difference is block flexibility.

H.264 uses fixed 16x16 pixel macroblocks. These blocks can be subdivided into 8x8 or 4x4 for detail areas, but the maximum size is always 16x16.

HEVC uses Coding Tree Units (CTUs) up to 64x64 pixels—16 times the area of H.264's largest block. These CTUs can be recursively subdivided into smaller blocks down to 4x4 pixels using a quadtree structure.

Why this matters in practice:

Picture a video frame showing a person standing in front of a white wall. With H.264, the wall requires dozens of 16x16 blocks, each encoded individually. With HEVC, a single 64x64 block can cover a large section of wall in one operation.

For the person's face (which has much more detail), HEVC subdivides into small blocks—8x8 or even 4x4—to capture fine features. The codec adapts its block size to the content automatically.

The result: fewer bits wasted on simple regions, more bits available for detail-rich regions.

Innovation 2: Advanced Intra Prediction

Intra prediction handles spatial redundancy within a single frame. When encoding a block, the codec looks at already-encoded neighboring blocks and predicts what the current block looks like based on surrounding patterns.

H.264 offers 9 directional intra prediction modes—essentially 9 angles from which it can extend neighboring pixels into the current block.

HEVC offers 35 directional modes. That's nearly four times the angular precision. This means HEVC can more accurately predict diagonal edges, gradual gradients, and textured patterns.

Real-world impact:

Consider encoding a frame of a sunset. The gradient from orange to purple involves subtle directional color shifts. H.264's 9 directions might not align well with the gradient angle, forcing the codec to encode the difference between prediction and reality (called the residual). HEVC's 35 directions can match the gradient angle much more closely, resulting in a smaller residual and a smaller file.

This improvement is especially noticeable in:

• Landscape and nature footage (lots of gradients and edges at various angles)
• Architecture (diagonal lines, patterns)
• Faces (subtle contours and shadows)

Innovation 3: Improved Motion Compensation

Motion compensation handles temporal redundancy—predicting the current frame based on previous (and future) frames. When an object moves, the codec doesn't re-encode it from scratch; it describes where it moved from.

HEVC improves motion compensation in several ways:

More flexible motion partitions. HEVC supports asymmetric motion partitions (like 12x16 or 4x12), allowing it to track motion boundaries more precisely. H.264 is limited to symmetric splits.

Quarter-pixel precision. Both codecs support sub-pixel motion estimation, but HEVC uses improved interpolation filters that produce more accurate predictions at fractional pixel positions.

Advanced merge and skip modes. HEVC can efficiently signal when a block's motion is identical to a neighbor's, reducing the overhead of motion information. In a slow pan where the entire frame moves uniformly, HEVC describes the motion once and applies it everywhere.

Innovation 4: Better Loop Filtering

After decoding, both codecs apply filters to reduce visible artifacts (blocking, ringing, banding). HEVC adds a new filtering stage called the Sample Adaptive Offset (SAO) filter that H.264 doesn't have.

The deblocking filter (both codecs) smooths block boundaries to reduce visible edges between adjacent blocks.

The SAO filter (HEVC only) classifies pixels by their local pattern and applies region-specific corrections. This is particularly effective at reducing banding in gradients—the visible "steps" in smooth color transitions like sky or fog.

For mobile video, where sky and smooth surfaces appear frequently, the SAO filter makes a visible difference in perceived quality at lower bitrates.

Innovation 5: Hardware Acceleration

Technical improvements only matter if they're fast enough for real-world use. HEVC encoding is computationally 2-3x more complex than H.264. On a CPU alone, this would make real-time 4K encoding impossible on a phone.

Apple solved this by building dedicated HEVC hardware into the A11 chip (iPhone 8, 2017) and every chip since. This hardware encoder:

• Encodes 4K 60fps in real time during camera recording
• Compresses video 5-10x faster than software encoding
• Uses a fraction of the battery compared to CPU-based encoding
• Maintains consistent quality because the silicon is purpose-built for HEVC

This hardware acceleration is why HEVC compression on iPhone is practical. Without it, compressing a 10-minute 4K video would take 30+ minutes and drain your battery. With it, the same operation takes about 5 minutes with minimal battery impact.

What This Means for Your Videos

All of these innovations compound into one simple outcome: HEVC stores the same visual quality in roughly half the space of H.264.

These savings apply automatically to new recordings (if your camera is set to High Efficiency). For older H.264 videos already in your library, compressing them to HEVC with HEVCut captures these savings retroactively.

The Bigger Picture: HEVC Enabled 4K on Mobile

Without HEVC, 4K video on iPhone would be impractical. A 128 GB iPhone recording 4K in H.264 would fill up in roughly 6 hours of recording. With HEVC, that same phone holds 12+ hours of 4K footage.

HEVC didn't just save storage—it changed what was possible:

• 4K became the default recording resolution on iPhone
• 60fps recording became practical without enormous file sizes
• Cinematic Mode was feasible because HEVC kept the combined video + depth data manageable
• Dolby Vision HDR recording was possible because HEVC handles 10-bit color efficiently
• iCloud Photo Library became usable for video-heavy users

Every major iPhone camera feature since 2017 was built on the assumption that HEVC would keep file sizes manageable. It's the invisible foundation of the entire modern iPhone camera experience.

FAQ

Is HEVC the same as H.265?

Yes. HEVC (High Efficiency Video Coding) and H.265 are two names for the same standard. Apple uses "High Efficiency" in iPhone settings. The video industry uses both terms interchangeably.

Can I tell the difference between H.264 and HEVC quality?

At the same file size, HEVC looks better (fewer artifacts, smoother gradients). At the same quality, HEVC is half the size. In either case, properly encoded HEVC is visually superior to H.264 for the same storage budget.

Why didn't H.264 just get improved instead?

The H.264 standard is frozen—no new features can be added. HEVC was designed from scratch to incorporate a decade of compression research that couldn't be retrofitted into H.264. The improvements (larger blocks, more prediction modes, SAO filtering) require fundamental architectural changes.

Does HEVC work on non-Apple devices?

Yes. HEVC is an international standard supported by virtually all modern devices: Android phones (2018+), Windows PCs, smart TVs, gaming consoles, and streaming platforms. Compatibility concerns that existed in 2017-2018 are largely resolved in 2026.

Will HEVC be replaced?

Eventually. H.266/VVC and AV1 offer 30-50% better compression. But the transition will take years—hardware support is still limited, and HEVC's ecosystem dominance means it will remain the practical standard for mobile video well into the 2030s.