Format overview

What are H.264 and H.265?

H.264, also called AVC, is a video compression standard used by cameras, streaming services, Blu-ray video, mobile devices, and web platforms. H.265, also called HEVC, is its newer successor and was designed to compress high-resolution video more efficiently.

Neither standard defines the file extension. An MP4, MOV, MKV, or transport-stream file can carry H.264 or H.265 video, so the container and codec should be checked separately.

Compatibility

Compression and quality differences

HEVC uses larger coding structures and more prediction options than H.264. At a comparable visual quality it can often use less bitrate, which is valuable for 4K, 8K, HDR, and storage-limited delivery. The tradeoff is higher encoding complexity and more demanding decoding.

Actual results depend on the encoder, preset, source material, resolution, and bitrate. A poorly configured HEVC encode is not automatically better than a well-configured H.264 encode.

How to compare one source fairly

Keep the source resolution and frame rate the same for both outputs so scaling or motion changes do not dominate the comparison. Compare clips with motion, fine detail, and dark areas at the quality and file size you can accept. Open both outputs in the actual destination; smaller files are useful only if picture, audio, subtitles, and seeking still meet your needs.

Playback also depends on the installed decoder. Microsoft explains how to check missing codec support in its Windows Media Player codecs FAQ.

Practical use

Which codec should you choose?

Choose the codec for the destination, not just the smallest file. Converting H.264 to H.265 normally re-encodes the video; a smaller output does not prove that quality was preserved.

  • Sharing and older devices: start with H.264 in MP4, then confirm the receiving app accepts its resolution, frame rate, and audio.
  • Storage on HEVC-capable devices: consider H.265 in MP4 or MKV after checking the supported profile, bit depth, and HDR handling.
  • Editing: use the editor-required profile or proxies when H.264 or H.265 playback is slow. A delivery codec is not always the best editing codec.
  • Keeping an already compatible stream: a supported copy or remux workflow avoids re-encoding. Changing the container cannot turn H.264 into H.265; see the FFmpeg streamcopy explanation.

Choose and verify the output in LosslessConverter

For an encoded file, open Output Format, select Video, and choose MP4 or MKV. Review the encoder and profile settings before converting. This is separate from Lossless > Multi-track MKV, which is intended for preserving supported source tracks rather than changing their codec.

Keep the original. Test a short representative clip in the actual destination and check picture quality, seeking, audio sync, subtitle behavior, and HDR appearance where relevant. Follow the video conversion steps and review supported outputs before processing a batch.