MKV, MP4, H.264, HEVC, 1080p… what do these video terms mean?
A video file is really several things packed together: picture, sound, subtitles, and the box that holds them. The string of abbreviations in a release name says which kind of each was used.
Container: mkv and mp4 are boxes
The file extension names the container — the format that bundles video streams, audio tracks, subtitle tracks and chapters. It says nothing about picture quality.
- MKV (Matroska): holds anything — any number of audio and subtitle tracks, attached fonts, chapters. Anime BDRips and fansub releases are almost all mkv.
- MP4: the most compatible (phones, browsers and TVs play it directly), but subtitle support is weak and only a few subtitle formats fit inside. Streaming and online-site videos are mostly mp4.
- WebM: a slimmed-down mkv for the web, holding only open codecs like VP9 / AV1.
The mkv and mp4 of the same show can have the identical picture — only the box differs.
Codec: H.264, HEVC, AV1 are compression methods
Raw video is far too big to store; a codec is the algorithm that shrinks it. Newer codecs give smaller files at the same quality but need more CPU / GPU to decode.
| Codec | Also known as | Notes |
|---|---|---|
| H.264 | AVC, x264 | Old and universal; every device decodes it in hardware |
| H.265 | HEVC, x265 | 30–40% smaller than H.264 at the same quality; the BDRip mainstream |
| AV1 | — | Smaller still, open and royalty-free; older devices can't decode it |
x264 / x265 in a release name are the encoders' names and mean H.264 / HEVC. Hi10P / 10-bit means each colour component is stored with 10 bits, so gradients (skies, shadows) don't band — anime encoders love it; older phones may lack hardware decoding for 10-bit H.264 and stutter.
Resolution: 1080p, 720p, 4K
The pixel dimensions of the picture. 1080p = 1920×1080, 720p = 1280×720, 4K / 2160p = 3840×2160; the p means progressive, the i in 1080i means interlaced, common in TV recordings.
Note that most Japanese anime is actually produced somewhere between 720p and 900p and the "1080p Blu-ray" is upscaled — a 720p BDRip is usually plenty to watch; 1080p mainly buys picture stability and crisper subtitles.
Bitrate: sharpness and size
Bitrate is how much data per second is spent on the picture, in Mbps. At the same 1080p, a 2 Mbps stream and a 15 Mbps BDRip look visibly different — dark scenes turning to mush and fast motion breaking into blocks are both signs of too little bitrate.
File size ≈ bitrate × duration: a 24-minute episode is a few hundred MB as a streaming WEB rip and one or two GB as a BDRip, and the difference is all bitrate.
Frame rate: 23.976 and 24
Frames per second. Anime is almost always 23.976 fps (a legacy of TV standards); some releases say 24. The gap is 0.1%, but if a subtitle was made for the other frame rate it drifts by several seconds over an episode — one of the usual causes of subtitles out of sync.
Audio: FLAC, AAC, 2.0 / 5.1
- FLAC: lossless, common in BDRips, large; AAC / Opus: lossy, used by streaming and small encodes; AC3 / DTS: older surround formats.
- 2.0 is stereo, 5.1 is surround. One mkv can carry both Japanese and English dub tracks, switched in the player.
For learning Japanese only the Japanese original track matters; the format doesn't.
An example
[VCB-Studio] Sousou no Frieren [01][Ma10p_1080p][x265_flac].mkvmkv container, 1080p, 10-bit (Ma10p), HEVC (x265), lossless FLAC audio. More on the other parts of a release name in reading release names.
What matters for Fushi
Fushi's player is built on libmpv and plays essentially every container and codec above. What to care about when picking a release is the subtitles: is there a Japanese text track in the mkv, is there an .srt / .ass next to it — see external, embedded and burned-in subtitles.