Why the Same Video Looks Different on Every Screen

You export a video, it looks right, and then somebody opens it on a different machine and the colours are wrong. Flat and grey, or too contrasty, or with a green cast that was not there before. The file is byte for byte the same file, so something in the chain is interpreting it differently.

This is one of the few video problems where the file really can be blameless and the fault really is elsewhere. Understanding what colour information a video carries makes it obvious where to look.

A video does not store colours

It stores numbers, plus a description of what those numbers mean. A pixel might be recorded as the value 180, and 180 is not a colour until something decides which shade of grey that is, how bright the display should make it, and what the primary red, green and blue actually are on the intended screen.

That description is metadata sitting alongside the picture, and it has three parts worth naming.

Get any of these wrong and the picture still plays perfectly. It just looks wrong, which is why this is so much more confusing than a file that refuses to open.

The washed out one: HDR shown as ordinary video

This is the common case now that phones record HDR by default. HDR footage stores brightness on a scale that goes far higher than ordinary video, and it relies on the player knowing that.

A player that does not understand HDR reads those numbers as if they were ordinary values. Everything that should have been bright lands in the middle of the range instead, so the picture arrives grey, flat and lifeless. Skin looks ill and skies look like fog.

The giveaway is that it looks correct on the phone that shot it and wrong everywhere else. That phone knows what it recorded; the other device was never told.

The fix is a proper conversion to ordinary range, called tone mapping, which remaps the bright detail into a range a normal screen can show. Simply stripping the HDR flag does not do this and makes the problem permanent instead of merely apparent.

The slightly green or slightly magenta one

This is a matrix mismatch, and it is nearly always the boundary between standard definition and high definition conventions. BT.601 was the rule for standard definition and BT.709 for high definition, and they separate colour from brightness in slightly different ways.

Decode one as the other and the picture is almost right. Skin tones drift, saturated reds and greens shift a little, and the whole image has a faint cast that is hard to name but obvious in a side by side comparison. Nothing is broken, one number in the header simply disagrees with what the encoder actually did.

The too dark or too bright one: levels

Video traditionally does not use the full range of available values. In limited range, black sits at 16 and white at 235 rather than 0 and 255, with the space at each end reserved for signal that overshoots.

If a player assumes full range when the file is limited, black becomes dark grey and the picture looks washed out and low contrast. If it assumes limited when the file is full, blacks crush to nothing and highlights clip, so shadow detail disappears entirely.

Screen recordings are where this bites most often, because a screen is a full range source being stored in a format that expects limited range.

How to tell which one you have

1. Play the file in two different players on the same machine. If they disagree, the file is fine and one player is interpreting it wrongly.
2. Read the file and note the colour primaries, transfer and matrix fields. If they are blank, every player is guessing, and different players guess differently.
3. Compare against the device that produced it. Correct there and wrong elsewhere points at HDR nearly every time.
4. Look at what specifically is wrong. Flat and grey is range or HDR, a colour cast is the matrix, crushed blacks are levels.

Missing colour metadata is a real defect even though it costs no quality. It leaves every player to guess, so the same file genuinely does look different in different places, and no amount of re-exporting fixes it until the tags are written.

What to do about it

If you are producing video for other people, tag it. An export with its primaries, transfer and matrix written correctly looks the same everywhere that respects them, and costs nothing but the flag.

If you are receiving video that looks wrong, do not colour correct by eye to compensate. You would be baking a fix for one player into a file that other players will then show incorrectly in the opposite direction. Work out which field is being misread and set it.

And if the source is HDR and the destination is not, convert properly rather than dropping the flag. Those are not the same operation, though they look similar in a menu.