H.264 and H.265 are two names for two closely-related things: the current widely-used video codec (AVC) and its successor (HEVC). The two codecs come from the same standards bodies (ITU-T Study Group 16 plus MPEG/ISO), use the same fundamental technique (block-based motion-compensated transform coding), and were developed a decade apart to solve exactly the same problem: fit more video into fewer bytes. HEVC does it about 40% better than AVC.

#The naming

  • H.264 = ITU-T H.264 = MPEG-4 Part 10 = AVC (Advanced Video Coding). Standardised in 2003. The workhorse codec of the modern internet - YouTube's primary delivery format for over a decade, the default of every consumer camera from 2005-2015, the codec every hardware decoder supports.
  • H.265 = ITU-T H.265 = MPEG-H Part 2 = HEVC (High Efficiency Video Coding). Standardised in 2013. Roughly 40-50% better compression at equivalent visual quality than H.264, at the cost of a more complex decode and a patent-pool situation that slowed adoption.

"H.264" and "AVC" refer to the same codec. "H.265" and "HEVC" refer to the same codec. The ITU number is what standards documents use; the MPEG name is what consumer marketing uses; the industry uses both interchangeably in casual conversation. Same technology, same encoded bitstream, same decoder chip.

#What HEVC does better

The technical improvement over H.264 came from three main areas: larger and more flexible coding tree units (up to 64x64 pixels vs H.264's 16x16 macroblocks), better motion prediction (asymmetric partitions, more reference frames, sub-pixel motion vectors at 1/4 accuracy for chroma), and better in-loop deblocking and sample adaptive offset filtering. Together these average to about 40% smaller files at visually-transparent quality - or the same file size at higher quality, or the same file size at higher resolution.

Practical example: a 5-minute 1080p clip encoded to visually-transparent H.264 lands at about 380 MB. The same clip encoded to visually-transparent HEVC lands at about 230 MB. On 4K content the gap widens further: 4K HDR HEVC content on streaming platforms is roughly half the size of the equivalent H.264 encode, which is why Netflix, Apple TV, Amazon Prime, and Disney+ all deliver 4K in HEVC exclusively.

#What H.264 does better

  • Universal decode support. Every device, every browser, every OS, every embedded player made in the last 15 years decodes H.264 natively without extra codec install. HEVC decode is universal on modern devices (post-2016) but still needs the HEVC Video Extensions app on Windows 10 and doesn't work reliably in Chrome on all platforms.
  • Faster software encode. H.264 encoding via libx264 is 2-3x faster than HEVC via libx265 for equivalent quality output. On machines without hardware HEVC encoders, H.264 is the practical choice for encode-heavy workflows.
  • Simpler patent story. H.264 has a single well-known patent pool (MPEG-LA). HEVC has three (MPEG-LA, HEVC Advance, Velos Media) with overlapping terms, which is the reason browser vendors stalled on shipping in-browser HEVC playback for years.

#The compatibility split, by device

  • iPhone / iPad (post-iPhone 6): Both codecs decode in hardware. iPhones record HEVC by default in High Efficiency mode (iPhone 8+).
  • macOS (Big Sur 11.0+): Both codecs decode in hardware. QuickTime Player, Safari, Chrome all play HEVC natively.
  • Windows 10: H.264 native; HEVC needs the HEVC Video Extensions app ($0.99, sometimes free via the OEM link). Once installed, every app that uses the OS decoder plays HEVC.
  • Windows 11: Both codecs decode in hardware; HEVC is included with the OS.
  • Android (post-2016): Both codecs decode in hardware on most devices. Cheap Android devices from certain manufacturers may skip HEVC decode - depends on the chipset.
  • Chrome on Windows/Linux/Android: H.264 native; HEVC only recently added (Chrome 107+ on desktops, spotty on mobile). Requires a supported hardware decoder path.
  • Firefox: H.264 native; HEVC not supported in the browser.
  • Smart TVs: Both codecs decode in hardware on any TV from 2016+; older TVs might skip HEVC.
  • Consumer video players (VLC, MPC-HC): Both codecs, all versions.

#Where H.265 wins in practice

  • iPhone camera storage. HEVC recording lets iPhone photos and videos take about 40% less space at the same visual quality. That's why Apple defaults to HEVC in the High Efficiency setting.
  • 4K streaming and download. Netflix, Apple TV+, Disney+, and Amazon Prime all deliver 4K exclusively as HEVC. Roughly half the bandwidth of an H.264 4K encode.
  • Blu-ray Ultra HD. Every UHD Blu-ray is HEVC. H.264 was never used for UHD Blu-ray - the bitrate math didn't fit.
  • Broadcast (ATSC 3.0, DVB-T2). Modern digital TV standards use HEVC because delivering 4K over broadcast bandwidth requires the compression efficiency.

#Where H.264 still wins

  • Everything sent to a stranger. If you're sharing a video via email, Discord, WhatsApp, or a website, H.264 is the safe default. Every recipient decodes it without extra install. HEVC works for most but not all.
  • Editing intermediate. Editors (Premiere, Final Cut, Resolve) work with H.264 more predictably than HEVC because H.264's decode is faster in software. ProRes or DNxHD are the actual editing-optimal codecs, but H.264 as a "reasonable file to edit" is more common than HEVC.
  • Live streaming. YouTube Live, Twitch, and every streaming CDN accepts H.264 with universal compatibility. HEVC live streaming exists but the encoder cost and decoder support are more constrained.

#The conversion between them

Converting H.264 to HEVC or HEVC to H.264 always requires a full re-encode - decode every frame, re-encode to the target codec. The visual quality trade-off depends on the encoder settings: a high-bitrate H.264 source converted to a similar-bitrate HEVC will be nearly indistinguishable from the source, but a low-bitrate HEVC converted to H.264 will show visible generation loss because H.264 at low bitrates can't match HEVC's efficiency.

Wave's re-encode path is H.264-only currently. When your source is HEVC and you need broader compatibility (older Windows viewers, embedded players), the /hevc-to-mp4/ page re-encodes to H.264 via the browser's WebCodecs encoder. When your source is H.264 and you want the file size drop of HEVC, HandBrake locally with the x265 encoder is the practical tool - no browser workflow ships HEVC encode natively yet (WebCodecs HEVC encode is in the spec but not widely available).

#The takeaway

H.264 and H.265 are consecutive generations of the same codec family. HEVC (H.265) gives roughly 40% better compression at equivalent quality, which matters for storage-limited devices (iPhones), bandwidth-limited delivery (4K streaming), and mass distribution (broadcast, Blu-ray). H.264 is universal - everything decodes it, everything encodes it fast. For sharing to strangers, H.264 is the safe default; for storing your own footage efficiently or delivering high-quality 4K, HEVC is the win. See H.264 vs HEVC vs AV1 for the full three-codec comparison including AV1 as the next generation.