4K Video Conversion: Codecs, Settings, and File Sizes

4K resolution means 3840x2160 pixels — exactly four times the pixel count of 1080p (1920x1080). This quadrupling of visual data creates a cascade of practical challenges: file sizes measured in gigabytes per minute, bitrate requirements that strain internet connections, encoding times that multiply by 4-8x, and storage demands that fill hard drives fast.

The promise of 4K is real — the additional detail is visible on large screens (50"+) at normal viewing distances, and the extra resolution provides headroom for cropping and stabilization in post-production. But the logistics of working with 4K video are fundamentally different from 1080p, and the codec choice matters more than ever.

This guide covers the real numbers: actual file sizes, actual bitrate requirements, what hardware you need for playback, and when downscaling to 1080p is the smarter choice.

4K File Sizes: The Reality

Here's what 4K video actually costs in storage, per codec:

The takeaway: H.264 at 4K produces impractically large files for storage and delivery. H.265 cuts the size roughly in half. AV1 cuts another 30%. For 4K content, using a modern codec isn't optional — it's a practical necessity.

For comparison: a 2-hour 4K movie at H.264 good quality is roughly 30-44GB. The same movie at H.265 good quality is 12-20GB. At AV1 good quality, 8-14GB. Netflix streams 4K at roughly 15-25 Mbps using their own AV1/VMAF-optimized encoding, producing about 14-22GB for a 2-hour film.

Codec Choice at 4K: H.265 is the Minimum

At 1080p, H.264 is fine — the file sizes are manageable, and the universal compatibility justifies the slightly larger files. At 4K, H.264's inefficiency becomes a real problem:

• H.264 at 4K: Needs 35-68 Mbps for good quality. This exceeds the bandwidth of many internet connections (the global average broadband speed is about 50 Mbps). Storage fills up fast. Not recommended for 4K.
• H.265 at 4K: Needs 15-30 Mbps. Comfortable for most internet connections. Reasonable storage requirements. Hardware decode available on all 2015+ devices. The practical default for 4K in 2026.
• AV1 at 4K: Needs 10-20 Mbps. Best compression but requires 2020+ hardware for efficient decode. Encoding is slow. Best for streaming services and web delivery where encode-once-serve-many economics apply.

Recommendation: Use H.265 for 4K content unless you have a specific reason for H.264 (legacy device support) or AV1 (web streaming at scale). H.265 provides the best balance of compression efficiency, encoding speed, and hardware decode coverage for 4K.

HDR at 4K: Formats and Considerations

4K and HDR (High Dynamic Range) are often bundled together, but they're independent technologies. HDR expands the brightness range and color gamut — brighter highlights, deeper shadows, more vibrant colors. The common HDR formats:

HDR and conversion: HDR metadata is fragile during conversion. The critical data points are:

• Color primaries and transfer characteristics — Must be preserved or the colors shift drastically
• MaxCLL and MaxFALL — Maximum content light level and frame average, embedded in the stream
• Mastering display metadata — The display characteristics used during grading

Converting HDR 4K video with FFmpeg requires explicitly preserving this metadata with flags like -color_primaries bt2020, -color_trc smpte2084, -colorspace bt2020nc, and copying the content light level data. Failing to do this produces video that plays but looks washed out or oversaturated.

When converting HDR to SDR (tonemapping): If the target device doesn't support HDR, you need to tonemap the video — compressing the wider dynamic range into SDR (BT.709). FFmpeg's zscale and tonemap filters handle this, but the results depend heavily on the tonemap algorithm chosen (hable, reinhard, mobius). There's no single "correct" tonemap — each makes different creative tradeoffs.

4K Encoding Time: Expect Hours

4K encoding is dramatically slower than 1080p because there are 4x more pixels to process:

Software H.265 encoding of 4K content is roughly 4-6x slower than real-time. A 1-hour 4K source takes 4-6 hours to encode with x265 at medium preset on a modern CPU (Ryzen 7 / i7 class). Hardware encoding (NVENC) is dramatically faster — the same 1-hour clip takes about 15-20 minutes — but produces files 20-30% larger.

Practical strategy: Use hardware encoding for quick exports and drafts. Use software encoding for final delivery where every bit matters.

4K Playback Requirements

Playing 4K video smoothly requires sufficient decode capability and display bandwidth:

Hardware decode:

• 4K H.264: Intel Skylake+ (2015), NVIDIA Maxwell+ (2014), AMD Polaris+ (2016), iPhone 6s+ (2015), Snapdragon 820+ (2016)
• 4K H.265: Intel Skylake+ (2015), NVIDIA Pascal+ (2016), AMD Polaris+ (2016), iPhone 7+ (2016), Snapdragon 820+ (2016)
• 4K AV1: Intel 11th-gen+ (2021), NVIDIA RTX 3000+ (2020), AMD RDNA 2+ (2020), iPhone 15 Pro+ (2023), Snapdragon 888+ (2021)

Display interface: HDMI 2.0 supports 4K at 60fps. Older HDMI 1.4 is limited to 4K at 30fps. DisplayPort 1.2+ supports 4K at 60fps. USB-C / Thunderbolt 3+ support 4K at 60fps.

Internet bandwidth for streaming: 4K streaming requires roughly 25 Mbps sustained (Netflix recommendation). 4K HDR requires 40+ Mbps. Many household internet connections share bandwidth across devices, making 4K streaming unreliable during peak usage.

When to Downscale to 1080p

Here's the uncomfortable truth: most viewers can't see the difference between 4K and 1080p on screens smaller than 50 inches at typical viewing distances.

At a 6-foot viewing distance (standard for a living room):

• Below 50": 4K is indistinguishable from 1080p for normal vision (20/20). The pixels are too small to resolve.
• 50-65": 4K provides a subtle but real improvement in fine detail.
• Above 65" or closer viewing: 4K is clearly visible and worthwhile.

For sharing video via email, messaging, or social media — where it'll be watched on a phone (6") or laptop (13-15") — downscaling to 1080p is free quality. The file is 75% smaller, encoding is 4x faster, and the viewer literally cannot see the difference.

When to keep 4K:

• YouTube (serves 4K to large-screen viewers)
• Archival (preserve the maximum resolution)
• Large-screen presentations (projectors, conference room displays)
• Post-production (4K gives cropping/stabilization headroom)

Convert and downscale: Convert from any format with resolution reduction: MKV to MP4 | MOV to MP4 | WebM to MP4.

Recommended 4K Encoding Settings

Container: MP4 for delivery, MKV for archival (supports all audio codecs including lossless FLAC).

Important: Always encode 4K with 10-bit color depth when using H.265 or AV1 — it eliminates banding in gradients (common in skies and dark scenes) and actually compresses slightly better than 8-bit because the codec has more bits to work with for gradual transitions.

4K is technically superior and practically demanding. The resolution increase is real and visible on large displays, but the infrastructure costs — storage, bandwidth, encoding time — are 3-4x those of 1080p. Modern codecs (H.265, AV1) make 4K manageable where H.264 makes it impractical.

The pragmatic approach: shoot in 4K for the quality headroom and archival value. Deliver in 4K only when the viewing context justifies it (YouTube, large screens, projectors). For everything else — email, social media, messaging, small-screen viewing — downscale to 1080p and save yourself and your viewers the bandwidth.