Choosing a Frame Rate on CCTV

Movies on film are almost exclusively projected at 24 FPS. Television, however, does not have an internationally accepted frame rate. In Europe and many other countries, PAL and SECAM use 25 FPS, whereas NTSC video in North America and Japan uses 29.97 FPS. Other common frame rates are usually multiples of these.

Note: Converting video formats from one frame rate to another is technically challenging, and there are often unwanted visual side effects. This is especially true when the frame rates do not evenly divide. For example, converting 30 FPS to 60 FPS is fairly easy to do, but converting 29.97 FPS to 25 FPS is much more difficult. Making sure audio stays in sync throughout the conversion is yet another challenge.

Some digital video formats support several frame rates within a single format, allowing variable frame rate video recording and film (24 FPS) compatibility.

Frame rate	Media	Description
24 fps	Film; high definition video	This is the universally accepted film frame rate. Movie theaters worldwide almost always use this frame rate. Many high definition formats can record and play back video at this rate, though 23.98 is usually chosen instead (see below).
23.98 (23.976) fps	Film; high definition video with NTSC compatibility; NTSC	This is 24 fps slowed down by 99.9% (1000/1001) to easily transfer film to NTSC video. Many high definition video formats (and some SD formats) can record at this speed, and it is usually preferred over true 24 fps because of NTSC compatibility.
25FPS	PAL; high definition video	The European video standard. Film is sometimes shot at 25 FPS when destined for editing or distribution on PAL video.
29.97 fps	NTSC; high definition video	This has been the color NTSC video standard since 1953. This number is sometimes inaccurately referred to as 30 fps.
30 fps	High definition video; early black-and-white NTSC video	Some high definition cameras can record at 30 fps, as opposed to 29.97 fps. Before color was added to NTSC video signals, the frame rate was truly 30 fps. However, this format is almost never used today.
50 fps	PAL; high definition video	This refers to the interlaced field rate (double the frame rate) of PAL. Some 1080i high definition cameras can record at this frame rate.
59.94 fps	High definition video with NTSC compatibility	High definition cameras can record at this frame rate, which is compatible with NTSC video. It is also the interlaced field rate of NTSC video. This number is sometimes referred to as 60 fps, but it is best to use 59.94 FPS unless you really mean 60 FPS.
60 fps	High definition video	High definition equipment can often play and record at this frame rate, but 59.94 FPS is much more common because of NTSC compatibility.

Important: Many people round 29.97 FPS to 30 FPS, but this can lead to confusion during post-production. Today, it is still very rare to use a frame rate of 30 FPS, but very common to use 29.97 FPS. When in doubt, ask people to clarify whether they really mean 30 FPS, or if they are simply rounding 29.97 FPS for convenience.

What is the NTSC and PAL Setting On DVR?

Many DVRs are compatible with both NTSC and PAL standards. NTSC standard is predominately in North America and PAL in Europe. The PAL and NTSC standard actually refer to the method used to transmit color. The PAL standard actually requires 2 NTSC decoders to display video (one for each line alternatively) while the NTSC standard only requires one. The NTSC standard is supposedly less accurate in color display, but more efficient in the use of resources. In general, the DVR can be set to either decode NTSC cameras or PAL cameras, but not a combination of both at the same time. If you order a DVR in a package with the security cameras, then you shouldn’t have to worry about the setting or compatibility. If, on the other hand you purchase your cameras from one country, and the DVR from another, then you definitely should make sure that the DVR is compatible with the cameras. Check the standard of the cameras (NTSC or PAL) and the standard of the DVR. Remember that you cannot mix and match the cameras.

Also, keep in mind that just because you are in the USA does not mean you cannot have a PAL DVR or PAL cameras, or because you are in Europe does not mean you cannot have NTSC cameras or DVR. In actuality, you only need to be sure that the cameras and DVR are both compatible.

RAW Formats

RAW Format implies that there is no compression done on the image. The major types of RAW format are RGB, YUV, YIQ. Our eye is more sensitive towards light intensity variation than color variation. So loss on color information will not affect the over all quality of the image. RGB is an end stream format. Information from the image sensor is in RGB format and we need the same format for displaying the image on an end

device. YUV & YIQ formats are developed for Analog TV transmission (NTSC & PAL respectively) and the digital version of YUV, YCbCr is the most common format used for image and video compressions.

Conversion from one format to another is described below:

RGB to YCbCr Conversion

Y = 0.299 R + 0.587 G + 0.11B

Cb = 0.564 (B - Y)

Cr = 0.713 (R - Y)

YCbCr to RGB

R = Y + 1.402 Cr

G = Y – 0.344 Cb – 0.714 C r

B = Y + 1.722 Cb

Y – Luminance Signal

Cb, Cr – Chrominance Signal, Color difference signal

R – Red

G – Green

B – Blue

Need for Compression

Consider an image of resolution 640 × 480. Let us calculate the size of the picture in RAW format. Each of the 10 Color is represented by 8 bits. Then for each pixel it needs 24 bits. Total no of pixels in the image is 640 × 480 = 307200 pixels. Therefore the size of the image turns to 307200 × 3 bytes = 921600 bytes. But an image in compressed format with the same resolution takes only 100 KB.

In the case of RAW video stream of length 1 sec its needs 640 × 480 × 3 × 25 = 23040000 bytes (23 MB) of storage if the frame rate is 25 frames/sec. But it’s known that the VCD format video having a size 700 MB plays for around 80 minutes. In the former case we need 110400 MBs (23 MB × 60 × 80) as storage space for 80 minutes video. Therefore we can achieve a high compression 150: 1 at the cost of computational complexities.