What do the properties of my video file mean?
Container, codec, bitrate, frame rate, pixel format and keyframes explained in plain words, using the Details tab in Cut by Zaweba as the guide.
A video's properties describe how it was packed, compressed and recorded. Cut by Zaweba lists them all in its Details tab: container, duration, size, bitrate, video codec with its profile and level, resolution, frame rate, pixel format, rotation, frame count, every audio track, subtitles and keyframe spacing. Here's what each one means and when it matters.
Cut is free software under the EULA and works offline, so you can inspect any file without uploading it.
The container and the codec
People often mix these up. The container is the box: MP4, MKV, MOV, AVI, WebM and so on. It's usually what the file extension tells you. Inside the box are separate streams of picture, sound and sometimes subtitles.
The codec is how each stream is compressed. H.264 is the most widely played video codec. HEVC (also called H.265) gives smaller files for the same quality but isn't played everywhere. VP9 and AV1 are common on the web. MPEG-4 and MPEG-2 are older. Two MP4 files can hold quite different codecs, which is why one plays on an old television and the other doesn't.
Profile and level are fine print on the codec. They say which features of it were used and how demanding the stream is. They matter mainly for older players, which may only handle certain profiles.
Size, duration and bitrate
Bitrate is how much data is used for each second of video, usually in kilobits or megabits per second. It's the main thing that decides file size: bitrate times duration gives roughly the size. Higher bitrate usually means more detail, though a modern codec does more with less. When Cut's For email preset aims to stay under 25 MB, it works out the bitrate from that target and the video's length, which is the same sum in reverse.
The picture
Resolution is the width and height in pixels, such as 1920 by 1080. Frame rate is how many pictures are shown each second; 25 or 30 is ordinary, 50 or 60 is smoother, and higher rates are used for slow motion. Frame count is the total number of frames.
Pixel format describes how colour is stored. Most everyday video uses a format that keeps brightness in full detail and colour at lower detail, because eyes notice brightness more. Unusual pixel formats can stop some players from showing a file.
Rotation is a note asking players to turn the picture. Phones use it instead of turning the pixels. A player that ignores it shows the video sideways.
Sound and subtitles
The Details tab lists every audio track with its codec, sample rate, channels, bitrate and language. Most clips have one track in stereo. Films and recordings from television may have several, such as different languages or a commentary. Subtitles are listed too.
Keyframe spacing, and why Cut shows it
Compressed video doesn't store every frame in full. A keyframe is a complete picture; the frames after it store only what changed. Keyframe spacing is how far apart the complete pictures are.
This matters for cutting. A lossless cut copies the original packets untouched, so it can only start on a keyframe. If keyframes are several seconds apart, a lossless cut may keep a few seconds more than you marked. Cut's Cut tab tells you how far apart they are for your marks and how much extra will be kept. If that's too much, a smart cut lands on the exact frame by re-encoding only the frames between each cut and the nearest keyframe.
Putting the details to use
Reading the properties answers practical questions. Why won't this play on the television? Check the codec and container. Why is the file so big? Look at the bitrate. Why does my cut start early? Look at the keyframe spacing. Why is it sideways? Look at rotation.
Cut by Zaweba opens MP4, MKV, MOV, AVI, WebM, WMV, MTS, M2TS, TS, FLV, GIF, M4V, MPG and 3GP. Text files and single pictures are turned away with a clear message, so you'll know at once if a file isn't a video at all.
