Video quality
Kitset encodes each video into several sizes, in two formats. A player starts with a size that suits the screen and the connection, then changes size as the connection changes. This is adaptive streaming.
The sizes
| Height | Format | Peak bitrate | Made for |
|---|---|---|---|
| 2160 | HEVC | 16,000 kbit/s | 4K sources |
| 2160 | HEVC | 9,630 kbit/s | 4K sources |
| 1080 | HEVC | 4,815 kbit/s | 1080p and 4K sources |
| 1080 | H.264 | 5,350 kbit/s | 1080p and 4K sources |
| 720 | H.264 | 3,210 kbit/s | Every source of 720p or larger |
| 480 | H.264 | 1,600 kbit/s | Every source of 480p or larger |
| 360 | H.264 | 856 kbit/s | Every source |
The peak bitrate is the upper limit of each size. Kitset aims at about 80 percent of the peak, and simple pictures use less.
Which sizes a video gets
A video gets each size that it can fill without enlargement. Kitset never makes a picture larger than the source.
- Each height has a 16:9 box, for example 1920 × 1080 for 1080. A source fills a size when it fills the width or the height of the box.
- So a wide source of 1920 × 800 gets the 1080 sizes at 1920 × 800, and a 3840 × 1608 source gets the 2160 sizes.
- A portrait source of 1080 × 1920 gets the 1080 sizes, because its height fills the box.
- A source that is smaller than 360p still gets the 360 size, at its own size.
Every size keeps the shape of the source. Kitset adds no black bars.
The Library shows the size of the largest rendition of each video, and its filter menu has a Resolution section: 2160p, 1080p, 720p, 480p and 360p.
The formats
- H.264 plays on every browser and device. Every video has its H.264 sizes first, so a player that supports only H.264 always finds a size that it can play.
- HEVC (H.265) gives a better picture at the same bitrate. Browsers and devices that can decode HEVC choose it, for example Safari on a Mac, an iPhone or an iPad.
Each video has two playlists: HLS (master.m3u8) and DASH (manifest.mpd). The player pages use both, and so can your own player. See Using videos on other sites.
HDR
When the source is HDR, the HEVC sizes stay HDR, in 10-bit colour with the transfer of the source (PQ or HLG). The H.264 sizes become SDR, with a tone map. So a person with an HDR screen and a player that can show HDR sees HDR, and every other person sees a good SDR picture.
The poster always comes from an SDR size, so it looks right on every screen.
The encoder
Kitset uses the hardware encoder of your Mac (VideoToolbox), so an encode is fast. A short clip often encodes in less time than it takes to upload. The files are a little larger than a slow software encoder makes at the same quality. For most sites, the speed is worth more than the difference.
- The frame rate of the source stays.
- Each size has a keyframe every 6 seconds, at the same times in each size. So a player can change size at each 6-second point with no jump in the picture.
- Kitset encodes all sizes in one pass of the source file, with the audio beside it.
The audio
Each video has stereo audio in AAC. A source with more than two channels also gets 5.1 surround audio. See Audio loudness.
Storage
The files of a video are about 5.8 GB for each hour of 1080p, and about 15 GB for each hour of 4K. Real sizes depend on the picture. The home page shows how to work out the cost.
What Kitset does not do
- No DRM. Anyone who has the link to a video can watch it and download its files. See Public and unlisted videos.
- No live streaming.
- No software encoders, such as x264, and no tuning of each video.