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22nd April 2013
New to digital camera video? Here's an introductory guide
by Ian Burley
9173: New to digital camera video? Here's an introductory guide

A basic introductory guide to video on digital stills cameras

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Practically all cameras currently on sale that are designed primarily to record stills images now include video recording options. This article is aimed at anyone who has not yet explored the wonderful world of digital video. It's not an in-depth technical article but instead it is a guide on how to get started and an explanation of the technology in an an easily digestible form that should help the reader get decent results straight away.

What is digital video?

Frame rate

In a sense you can regard digital video as a serious of still images taken by the camera at a fairly high frame rate. These are recorded as a sequence in a file and played back at the same rate they were recorded at. There are several frame rates you may or may not be able to use. Perhaps the most common is 30 frames per second (fps). This is especially useful for people in countries where TVs and the electricity supply work at 60Hz, which is double the rate of 30fps (well, actually that may not be the case but we'll cover this later!). 25fps is an alternative for users in countries where the AC electricity frequency is 50Hz, along with TV displays at the same rate. A key reason why you want be recording at a frame rate that is a factor of the electrical frequency is to avoid an unpleasant strobing effect under artificial lighting. And then there is 24fps, the frame rate used for filming and the standard for Hollywood movies. Some say that 24fps looks more film-like. Bur in simple terms you really need to know what you will be processing your footage for if recording at 24fps. If your recording frame rate also differs fractionally from the rate at which the video will be replayed there will be a jerkiness to action during playback as frames are dropped. Only a few cameras offer the full range of frame rates. The higher the frame rate the higher the rate at which your memory card storage will be consumed. Just to complicate matters, 30fps video is usually more precisely 29.97fps.

Progressive or interlaced?

Progressive video sees a whole frame played at a time. Interlaced video involves playing only half a frame, or more accurately one of two fields that make up a complete frame, at a time, but not by splitting the frame down the middle. Instead, video resolution is described in lines (horizontal and vertical). With interlaced video alternating horizontal lines contain detail from one frame field, or half of the frame, and the other alternating lines contain the second field or second half of the frame. When an interlaced video is played back optimally the human eye doesn't see the two sets of alternating lines, or fields, being combined to complete the frame. This is because at 50Hz or 60Hz the eye is fooled into seeing smooth motion. Progressive video can be denoted by the letter 'p', for exampled 720p (720 horizontal lines played in progressive mode). Interlaced video is denoted by the letter 'i', for example 1080i (1080 horizontal lines played in interlaced mode). Why is interlaced video used? Because it can be used mimic a higher frame rate without increasing the amount of data, or bandwidth, being played. If viewed in a CRT (TV tube) or plasma display, interlaced video can look very good. LCD displays will usually de-interlace the playback so the frame rate looks slower.

The problem with interlaced video playback is that very fast movement can cause a momentary break up of picture detail and this becomes worse with poor quality video, often with ugly artefacts appearing where movement is prevalent in the frame. Even with static detail, especially very high contrast fine details, interlaced playback can cause an instability that can be uncomfortable when viewing. In general, progressive video is preferable but requires more processing power at higher frame rates, so high frame rate (50 and 60Hz) progressive video recording is generally a premium feature on more expensive cameras.

Resolution

Most cameras offer lower quality video recording at VGA (640x480 pixels) resolution. High Definition (HD) video exists in two widely supported resolutions: 720HD (1280x720 pixels) and 1080HD or 'full HD' (1920x1080 pixels). An immediate problem with VGA resolution video is that it's not 'wide screen' format, so when played back on a modern TV or computer screen there will be black bars on either side of the frame, which won't be the case with HD resolutions. HD video resolutions do consume more storage space than VGA, but the only reasons I can think of for using VGA resolution video recording is if you have a specialist need for it or if you are low on memory card storage space.

Video formats

The most common video recording format in stills camera is motion JPEG, or MJPEG. This is a simple adaptation of the JPEG format used in stills images, which records a sequence of JPEG stills in a single motion video file. MJPEG is technically simple and although it is not very efficient in terms of data compression, picture quality is very good, especially for video in which there is a lot of action in the footage. But that data compression inefficiency is a serious drawback for HD video. Even at the lower resolution 720HD resolution, video clips lasting just 5 or 6 minutes might consume as much as 2GB of storage space. MJPEG video is often encapsulated in an AVI file and when recorded by most digital cameras onto flash memory cards the maximum size of an AVI file is 2GB. If you are restricted to sequences not much longer than 5 minutes is a real problem at times.

More efficient compression schemes, like H.264, mean that much larger file sizes can be recorded and more footage minutes can be recorded per GB. Acronyms like MPEG4 and AVCHD, as well as H.264, abound. Because of the way in which video standards have developed and evolved the exact definitions of these terms are increasingly difficult to determine. MPEG4 and H.264 have both been around for a long time but MPEG4 now encompasses H.264 technology and the AVC(HD) standard invented by Sony and Panasonic embraces both. It would take a huge technical article to unravel the many differences and similarities of these standards so we'll just concentrate on the most relevant.

H.264 This is a very efficient video compression system and is widely supported. H.264 videos. H.264 video is not saved in an H.264 file format. Instead, it is package or encapsulated in a file container, along with the audio track and maybe metadata about the camera and time, recorded, etc. The container file could be a .MOV (QuickTime), .MP4 (MPEG4) or other file type. Some regard H.264 files as more user-friendly to use and edit.

AVCHD is a digital video format created and developed by Panasonic and Sony. It employs technologies from both H.264 and MPEG4. AVCHD exists in a number of forms and since 2011 supports 3D video . Being a relatively recent standard, AVCHD did not enjoy widespread support in video editing software for a while, but that has mostly been solved today. Due to its high degree of complexity, AVCHD requires a lot of computational power to encode and decode, which means performance when editing using an older and slower computer has been noted as problematical. AVCHD videos are recorded as .MTS (MPEG Transport System) files. Cameras supporting AVCHD also build a relatively complex file and folder structure on the recording media which hides away the actual .MTS video files. Typically, to find recorded .MTS video files you need to navigate PRIVATE > AVCHD > BDMV > STREAM. Note: some video editing software applications require that you present the original multilevel folder and file structure rather than the individual .MTS file clips.

Recording length limits

In some countries there is an additional import levy on cameras that can record video sequences of 30 minutes or longer. This means that camera manufacturers deliberately limit their cameras' recording capability to less than 30 minutes.

Bit rates

A crude measure of the quality potential of a digital video camera is the video bit-rate. In theory a camera that can generate a higher bit-rate should be able to record more image data per second and so a better quality - as long as that data is not something like noise, for example.

Rolling shutter or 'jello' effect

You may have noticed some videos, especially where the camera moves a lot, which exhibit an unpleasant instability that is akin to that of a wobbling jelly. This is the infamous rolling shutter effect which is not seen in older cameras that use CCD sensors as opposed to more widely used CMOS or NMOS type sensors these days. In a CCD sensor the image is frozen before its entirety is read off and then the sensor is reset ready for the next frame. This is called global read-out. In MOS-type sensors each pixel is read individually and line by line. Let's assume that the read-out starts at the top line and progresses line by line down the frame until it reaches the bottom. Think of a vertical line in the frame, like the side of a building; if the camera panning to one side, by the time the read-out reaches the bottom of the frame the side of the building will have moved across the frame to a degree. The recording of the position of the side of the building at the top of the frame will no longer line up with the position at the bottom of the frame. The entire building geometry will be distorted as if it has become flexible and it will appear to be leaning to one side. If you watch video footage where the camera is panned left and right repeatedly the effect can be amplified and nothing will look solid any more. A key tip for avoiding this is to minimise the speed at which you move the camera, especially when panning. In some cases, image stabilisation can help, especially where small movements of the camera which is not being moved deliberately can cause a more subtle picture instability. Some cameras exhibit more of a 'jello' effect than others, dependent on how fast the frame read-out can be performed.

Image stabilisation and focusing

Image stabilisation and auto focusing need to work differently when recording video compared to shooting stills. This is especially the case with focusing. With stills you want the AF system to snap to best focus as fast as possible. With video, however, the focus changes need to be very gentle and smoothly delivered. I have read camera reviews where focus speed was criticised in video mode but this is clearly missing the point. Image stabilisation also needs to be unobtrusive and it needs to be active all the time if you choose to use it. In reality not all cameras offer a video-mode for AF, so it's worth learning if your camera or combination of camera body and lens does. In still photography the optimal image stabilisation mode often sees the system activate only as you press the shutter release.

What to do with your video footage?

Apart from viewing recorded footage on the screen on your camera or on your computer screen, here are some other possibilities:

Connect your camera directly to your TV. Most recent cameras now support direct cable connections to modern TVs using an HDMI cable. This is usually via a Mini-HDMI port on the camera although some cameras have a smaller HDMI port and some smartphones use the same port that is used for USB connection and battery charging. If your camera is compatible with HDMI-CEC (Consumer Electronics Control) you may be able to configure your TV so that its remote control can also control your camera when it is connected to the TV via HDMI.

Upload videos to YouTube, Facebook, Flickr and other social media sites

Many online social media networks now positively encourage videos to be uploaded. The obvious site to upload video to is YouTube. It's possible to upload unedited and unconverted video clips straight to YouTube, who will then convert the footage for playback on your channel in YouTube. You can also add captions and links to your videos on YouTube, which also offers a option to address camera shake in videos. Vimeo is another online video hosting site worth considering and many say that videos play back better from Vimeo. However, YouTube is completely free and you can even earn ad revenue if you video becomes popular. Vimeo can be free but there are limitations like a maximum full size of 500MB, for example. To overcome such limits you can go for a paid account.

Edit your video and make video productions

There is nothing like producing a movie from several clips, with nice inter-scene effects like fades or wipes, adding captions and music, etc. Results can then be burned to DVD or uploaded for viewing later. There are many video editors to choose from, like Adobe Premiere Elements or the full-blown professional quality Adobe Premiere CS6. One particularly good value package is CyberLink PowerDirector 11, which can utilise GPU power from some CPUs as well as graphics cards for faster video rendering. Others worth considering include Corel VideoStudio Pro X6, Magix Movie Edit Pro, and Sony Movie Studio.

To finish off

Video is a big area that will take years for most of us to really master. There is no substitute for getting the camera out and simply experimenting and that in itself can be a lot of fun!

Reader feedback:

Discuss this story:

New to digital camera video? Here's an introductory guide

DPNow New to digital camera video? Here's an introductory guide
H Practically all cameras currently on sale that are designed primarily to record stills images now... (more)

Bob Ross Re: New to digital camera video? Here's an introductory guide
Hi Ian, This is a very useful article for me, even though I'm not inclined to do movies with all th... (more)

Ian Re: New to digital camera video? Here's an introductory guide
Hi Bob - don't worry, you will soon have hours of footage - literally, taken as the camera is restin... (more)

patmoore Re: New to digital camera video? Here's an introductory guide
Great article Ian! I learned a lot from it. I shoot a great deal of and have tried many different... (more)

Bob Ross Re: New to digital camera video? Here's an introductory guide
Hi Ian, The accidental Indy Movie hazard seems to be inherent to the smaller form factors with the ... (more)

patmoore Re: New to digital camera video? Here's an introductory guide
I just re-read the article and found it very helpful with understanding my newly acquired Panasonic ... (more)

 
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