Video & Associated Formats

The video enthusiast, when he/she first starts editing, is sometimes confused about the various formats that he will encounter. This page aims to clarify this subject, and to clear up some misconceptions.

There are several different (but associated) format categories:

• TV display formats
  
  
• PC display resolution
  
  
• Recording media formats
  
  
• Compression formats

Camcorder recording formats include 8mm, Hi8, and DV (Digital8 and miniDV). There are also camcorders still in use that use VHS-C and VHS, so these are included here. Because of the existence of S-VHS we'll also include those here.

Professionals use a variety of formats, but since this site is about consumer camcorder, I've not included them here.

TV Display Formats

Its important to appreciate that whatever recording format we're using, the display on TV is by either PAL or NTSC. The significance of this is that the picture is displayed as a number of horizontal lines on the TV screen, 625 lines for PAL or 525 lines for NTSC. There are also other display standards, e.g. SECAM - but that is not included here. The display (or raster) lines are interlaced (i.e. two scans per picture frame) so that the horizontal scan lines are not apparent to the viewer.

PC Display Resolution

PCs on the other hand have the potential to display at the vertical pixel count (equivalent of raster lines) of the display monitor, typically 600 (800x600) 800 (1024x800) lines or even higher.

Quality

The "quality" of a picture comprises many elements: resolution, colour accuracy, and artifacts, to name just three.

Line Resolution

A lot of video beginners equate raster lines with (line) resolution - they are not the same.

To understand line resolution it helps to remember just how it it determined. A test card with a number of blocks of vertical lines of various line widths (the spaces being the same as the lines) is shot and recorded on the media being tested. So if the vertical lines in the block containing 240 lines can be seen when replayed, while those in the block containing 250 lines can not be seen then the "line resolution" is 240 lines This is the figure for VHS). Thus there is often confusion between raster (or scan) lines and line resolution.

Recording Media Formats

Now that we appreciate just what line resolution actually is, lets see what the various recording formats can achieve. The table below shows the line resolution as well as other characteristics associated with the various recording formats.

Recording Format	Lines Resolution	Audio	Tape Type	Tape Width	Signal Type
VHS	240 lines	1 linear; 1 stereo AFM (Hi-Fi)	Oxide	0.5 inch	Composite
VHS-C	240 lines	1 linear; 1 stereo AFM (Hi-fi)	Oxide	0.5 inch	Composite
8mm	260 lines	1 stereo AFM; 1 stereo PCM	Metal Particle	8mm	Composite
Hi8	400 lines	1 stereo AFM; 1 stereo PCM	Metal Particle	8mm	Y/C
S-VHS	400 lines	1 linear; 1 AFM (Hi-fi)	Oxide	0.5 inch	Y/C
Digital8	500 lines	(2) 16-bit; (4) 12-bit PCM	Metal Evaporated	8mm	Component Digital
MiniDV	500 lines (see Note)	(2) 16-bit; (4) 12-bit PCM	Metal Evaporated	6mm	Component Digital
DVD	480 lines	Note: DVD is digital and uses MPEG-2 compression, which is lossy.

Note: Sony claim 530 lines on miniDV camcorders models incorporating their HAD technology with 16-bit
signal processor. You should also be aware that shooting in low light (no matter what the manufacturer claims) results in a substantial loss of quality - though this is unrelated to the recording media.

The lesson we can learn from the second column in the above table is that once we transfer our video to (say) VHS, we can never restore the resolution back to that of DVD. The same is true (to a lesser extent) for DVD.

In the Audio column, AFM stands for Audio Frequency Modulation and PCM stands for Pulse Code Modulation. You'll also note in the Audio column that both Digital8 and MiniDV provide the capability to provide either two-channel or four-channel audio; the higher 16-bit option allows higher quality audio.

In the Tape Type column, Oxide tapes limit the upper frequency that can be carried (hence resolution is relatively low), and are more prone to shedding particles than are the other tape types. Metal Particle tapes are better in both particle shedding and in upper frequency response. The best is Metal Evaporated in both respects.

The last observation to be made in the above table is that DVD is not the highest resolution and (using MPEG-2) it is lossy. The latter means that if you burn a DV movie onto DVD, and then retrieve that movie and convert it back to DV, the quality will be reduced. More importantly, if you repeatedly do this, the loss of quality is cumulative.

This leads to the major advantage of DV, that no matter how many times your copy DV-to-DV, you'll lose no quality. This is the reason why I recommend that you "master" all your movies and save them back to miniDV using your camcorder, then use your master to dupe your movie to VHS, CD, VCD or DVD for distribution. The way that you do this depends on your camcorder - most (all) DV-in Sony camcorders have an unmarked button next to the REC button, which, when pressed with the REC button, causes the firewire DV-in signal to be recorded to tape (rather from the lens/CCD).

Compression Formats

Distinct from the media format is the compression format (though each media type is usually associated with a particular compression format). The table below summarises the media/compression format relationships - and the resulting quality when replayed from the media.

Video	VCD	SVCD	DVD	AVI	DivX	ASF
Video Compression	MPEG1	MPEG2	MPEG2	Uncompressed	MPEG4	MPEG4
Audio Compression	MPEG1	MPEG1	MPEG2	Uncompressed	MP3/MPA	MPEG4
Size 1 hour video	600 MB	about 1 GB*	about 2 GB*	several GBs	about 350 MB*	about 120 MB*
Quality	Good	Great	Excellent	Excellent	Good	Bad
* = it depends on the audio and video bitrate.

AVI - A Special Case

AVI requires a little explanation since it isn't a compression standard, but rather a "container" for the storage of data of any type - and most operating systems provide the means to display it.

It is possible for an AVI file to "contain" MPEG-1, MPEG-2, MPEG-4 compressed or DV itself within an AVI file - but the filesize is only marginally greater than the size of the associated content (see Size 1 hour video in the table).

All video editing programs on sale today support AVI 2 - which places no filesize restriction on a video file (though the operating system version may limit the maximum filesize). You may, however, encounter older "legacy" video editors (or other software) that only support the original AVI (now known as AVI 1) - which limits filesize to 2GB..

Operating/Filesystem Restrictions

Some Windows versions impose a filesize restriction as shown in the table below.

Operating System/Filesystem	16-Bit	32-bit	NTFS
Windows 3X	2GB
Windows 98	2GB	4GB
Windows 98SE	2GB	4GB
Windows 98 ME	2GB	4GB
Windows 2000		4GB	Unlimited
Windows XP		4GB	Unlimited

Archiving DV

DV provides us with a compression format that provides:

• The best possible quality
  
  
• An almost lossless compression
  
  
• Large filesize (3.6MB for each second of video)

Obviously, it is best practice to archive not only our source video (which presents no problem since its already on miniDV or Digital8 tape), but our movie "master". The reason for archiving our finished movie in DV is that if we write our video to (say) VHS (or even burn to DVD as MPEG-2), the quality is reduced as shown in the Recording Media Formats table. Worse, if we duplicate our video from these lower-quality recordings, the quality is further reduced since the "loss" of quality is cumulative..

Archiving DV to DVD can be done by containing the DV in an AVI file, but you are limited to about 4GB (about 20 minutes of video.

The only solution currently available if we wish to maintain the highest possible quality in our movie master is to "write-back" to the camcorder's miniDV or digital8 tape. To do this our camcorder must have the DV-in facility.

I hope this page has been of interest (and hopefully of value) to video enthusiasts. I have tried to keep it as simple as possible without getting too technical.

---