§ 19

Video recording: storage space and card

How much space does the recording take up, and how long can a card hold?

Answer: With video, it is the bit rate, not the image size, that determines how much space the recording takes up. Enter the camera's bit rate (it is in the recording menu, e.g. 100 Mbit/s for 4K XAVC S), how many minutes you record, how many cameras are running, and the card size. Then you know how many cards and how much backup space the job needs.

Formula

GB = bitrate (Mbit/s) × sekunder ÷ 8 ÷ 1.000

Minutter pr. kort = kortets GB × 1.000 × 8 ÷ bitrate ÷ 60

1 byte = 8 bit. Kort- og diskproducenter regner 1 GB = 1.000 MB.

Symbols and units in the formula
Symbol	Meaning	Unit
bitrate_mbps	Camera bitrate	Mbit/s
minutter	Shoot time per camera	min
kameraer	Number of cameras	stk
kort_gb	Card capacity	GB
=	Storage space in total	GB
=	Storage space per camera	GB
=	Shoot time per roll	min
=	Card per camera (whole card)	kort

Validity and source

Source: Forholdsregning · bitrate i Mbit/s, 1 byte = 8 bit, 1 GB = 1.000 MB

Does not apply when

The camera often shows slightly less free space than the card's marking (file system and binary GB). Audio in a separate recorder and proxy files come on top. The backup must be able to hold at least as much again.

Worked example

The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.

Substituted

Camera bitrate100 Mbit/s
Shoot time per camera90 min
Number of cameras2 stk
Card capacity128 GB

Giver

Storage space in total135.0 GB
Storage space per camera67.5 GB
Shoot time per roll171 min
Card per camera (whole card)1 kort

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Sådan bruger du den

Ved video fylder optagelsen efter bitraten, og det går hurtigt med 4K. Før en konference, et bryllup eller en reklamefilm skal du vide, hvor mange kort du skal have med, og hvor meget backup-plads opgaven kræver bagefter.

Step by step

Find bitraten i kameraets optagemenu eller manual, fx 100 Mbit/s for 4K i XAVC S.
Gang bitraten med optagetiden i sekunder, og del med 8. Så har du megabyte.
Del med 1000 for at få GB pr. kamera, og gang med antal kameraer.
Del kortets kapacitet med forbruget for at se, hvor mange minutter et kort holder.

Typical errors

At forveksle Mbit/s og MB/s. Bitraten står i bit, og der går 8 bit på en byte.
At glemme at kortet også skal kunne skrive hurtigt nok. Høj bitrate kræver V60- eller V90-kort.
At regne med kortets fulde mærkning. Kameraet viser altid lidt mindre ledig plads.

Examples from everyday life

Konference med to kameraer

Du optager en konference på 90 minutter med to kameraer i 4K på 100 Mbit/s og 128 GB-kort.

Camera bitrate: 100 Mbit/s
Shoot time per camera: 90 min
Number of cameras: 2 pcs
Card capacity: 128 GB

It means: Optagelsen fylder 135 GB i alt, 67.5 GB pr. kamera. Et kort holder 171 min, så du skal bruge 1 short pr. kamera. Backup-disken skal mindst kunne rumme det dobbelte.

Bryllupsfilm i høj bitrate

Til en bryllupsfilm optager du i 4K 10-bit på 200 Mbit/s med ét kamera i alt ca. 4 timer og har 128 GB-kort.

Camera bitrate: 200 Mbit/s
Shoot time per camera: 240 min
Number of cameras: 1 pcs
Card capacity: 128 GB

It means: Optagelsen fylder 360 GB. Et kort holder kun 85 min, så du skal have 3 short med og skifte i pauserne.

Rule of thumb

100 Mbit/s fylder ca. 45 GB i timen. Fordobl bitraten, så fordobles pladsen.

How to check the answer

Optagetid pr. kort gange bitraten gange 60 og delt med 8000 skal give kortets GB.