Updated May 12, 2009   

Video Guides > Capturing/Recording > Introduction to Recording Digital Video

Article last updated 2006

Capturing video is not as simple as installing a capture card, plugging a VCR into it, and hitting the "go" button in the software that came in the box. Even something as simple as driving a car took a little bit of education.  

An effective video capture requires the following forethoughts and decisions:
- What capture card? 
- What capture software?
- What is the source? And what capture resolution?
- MPEG or AVI? To edit or not to edit? 
- If MPEG, what bitrate?

Each of these factors must be understood and considered. Your capture hardware/software and capture settings/format must reflect BOTH the source video and end-goal of the video project. Unlike some guides, this is not a 1-2-3 connect the dots kind of guide. It is not a flow chart, but rather a list of concepts, each equally important, and each one relating to all the other concepts. Read the ENTIRE PAGE before acting on the information.

Capture Cards (Examples)

It may seem like a simple question, but it's really not. What capture card? Although readers of this guide may already own a capture card, this topic is integral to the overall topic. And capture software depends entirely on the card that is selected. If you own a card that does not accomplish your goals, considering changing to a new card. 

Something to keep in mind is: Can your card properly capture the format/resolution you are considering? Capture cards are preset to capture a certain resolution, and then internally processes/resizes the video, as asked for by the software. The hardware is also hardwired to output a certain video format (AVI or MPEG) and then any changes to this are done completely in software. Your goal should be to identify the native card resolution, the output format, and then use that knowledge to your advantage.

For the purpose of this guide, there are essentially FIVE TYPES of capture cards:

Capture Software (Examples)

A capture card is only as good as the capture software. Remember to select a capture software does not harm the incoming signal, but rather encodes or transfers it as needed. Capture software often has the ability to both filters and re-encode the video to the desired codec or MPEG format. Much like capture cards, the quality of software varies greatly, from excellent to complete rubbish. Your goal is to use software that complements your card, in the pursuit of high quality video captures.

What is the Source? And What Capture Resolution?

The UNDERSTANDING YOUR SOURCE capture guide has detailed information on source files. However, the following quick-list will cover the suggested capture resolutions for the most common sources, sorted by resolution:

352x480 = VHS, S-VHS, 8mm, Hi8, Betamax, most of satellite, cable, broadcast antenna
480x480 = anything being converted directly to SVCD
640x480 = anything being captured as AVI intended for advanced editing in an NLE
704x480 = laserdiscs, Betacam SP, PPV satellite channels
720x480 = laserdiscs, Betacam SP, PPV satellite channels

Suggested AVI capture resolution. If you plan to heavily edit to video, experience has shown capturing at 640x480 or 720x480 resolution will often yield the best final product. It may be a huge file, but if quality is important, you'll find a way to store it. You can resize to a smaller resolution when encoding the final MPEG.

Suggested MPEG capture resolution. Since MPEG is a final output format, it is best to capture at the size and bit-rate you plan to use in the final project. Capturing 352x480, 704x480 and 720x480 all look fine for DVD. Capturing 352x240 can look fine too (though no suggested), depending on the program and it's method of on-the-fly de-interlace. All 352x240 captures should be MPEG-1. Though MPEG-2 should look the same in theory, it often does not, with a lot of macroblocks as compared to the MPEG-1 version at the same resolution and bit-rate. Plus most capture programs and even authoring programs do not accept MPEG-2 352x240 source. Only do 352x240 if you plan to directly burn to VCD or low-quality DVD. Capturing 480x480 for direct-to-SVCD projects is fine too.

Digital resolution notes:
- Interlace barrier. Most traditional source is interlaced video. The interlace barrier for digital video is approximately x280 resolution. This means that interlace can only be achieved at a spec resolution above that number. In the MPEG world, this can be x288 and x576 in PAL or x480 in NTSC. 
- PAL 288 interlace. While you can capture/encode x288 interlaced, it is not suggested and indeed not officially supported for the VCD or DVD spec. Plus it is well below the true resolution of the source.
- VCD resolution does not equal VHS resolution. That is a myth perpetuated by misinterpretation of analog "lines of resolution" and how it fits into the digital realm. While 240 is a number used in both the VCD resolution and VHS lines of resolution, they represent opposite axes. VHS is also interlaced while VCD is progressive.


MPEG or AVI? 

All too often, videographers and hobbyists make this appear to be a harder choice than it really is. Choosing AVI over MPEG, or MPEG over AVI, is a simple choice to make, and should take maybe 10 seconds to decide. 

Ask yourself this one question: Do you plan to do advanced editing* with the video? 
= If yes, then use an uncompressed (YUY2) or low compression (HuffYUV or MJPEG) codec using the AVI file format. Use this AVI to edit in your favorite editing program (like Adobe Premiere) and then encode to MPEG-2 (for DVD) or other desired final format.
= If no, and you merely want to convert the video to VCD or DVD format, then encode directly to MPEG-1 or MPEG-2. You gain no benefits** by capturing AVI then encoding to MPEG afterwards. In fact, all it does is take more time. 

* Removing commercials and cutting away unwanted footage is NOT considered advanced editing. That is basic cutting and splicing of footage. You can do this with either AVI or MPEG without reconverting the video or harming quality. 
** Capturing in MPEG format assumes you have a decent MPEG capture card and capture program, such as an ATI All In Wonder card using ATI MMC. Many cards and many software give poor MPEG capture results. Non-ATI users can try other programs, but the options are few and disappointing. This is the main reason I suggest ATI cards. Cards like Matrox, Canopus and Hauppauge can also give great results, using their supplied software.

Note: Capturing in high compression codecs, like that of XVID, QuickTime or Windows Media, is not suggested. It will give lower quality video output using that method. For best results, capture with an uncompressed or low-compression codec, and then re-encode the material to the higher compression ratio. 

More on the AVI format

History and basics. AVI is one of the oldest video formats still in common use, having been created by Microsoft more than a decade ago. An AVI is an Audio-Video Interleave based on RIFF headers (resource interchange file format). For years, it was the only viable digital video format available. 

Codecs. An AVI is actually not a video format. The "AVI" file is merely a wrapper, what I like to call a "container" file. It holds video and audio information that would typically be unable to exist as its own file format. This video and audio information is written to and read from the AVI by codecs (compressor-decompressor files). Popular codecs include MPEG-4, DivX, Xvid, MJPEG, HuffYUV, and other FourCC variations. Even MPEG and Windows Media Video (WMV) can exist within an AVI file, as the AVI is just video data with a RIFF header surrounding it. 

Drawbacks. The AVI format has several distinct drawbacks, with the major one being huge file sizes when using no- or low-compression codecs. (Older variations of AVI present in Windows 3.x and Windows 95/98/NT4 had limitations that prevented file size of larger than 2GB or 4GB, however that has since been removed with the newer operating systems and updates for 98/NT4.)

Temporary only. Most AVI codecs are intended only as temporary working format, not meant to be final products. An AVI typically serves no purpose outside of an editing environment on a computer using Windows. It has little compression applied, and can easily be manipulated a few times before degradation occurs to the video information. This is opposite of television/DVD formats like MPEG, and streaming formats like QuickTime, RealMedia and WMV, all of which are end-product formats. Apple uses Sorenson-based QT files as their working format.

Myths. An AVI is not any better than an MPEG. It is just different. In fact, using a low bit-rate DivX codec AVI encode will always look worse than a high bit-rate MPEG. Quality depends on how you use the files. As has been stated earlier in this section, if editing is not needed, then capturing directly to MPEG is acceptable and quality will be just fine, assuming the capture card and capture program are decent. This is why most people assume MPEG is worse: their hardware and software is not great. Be aware that many of the so-called "lossless" codecs are still quite lossy.

More on the MPEG format 

History. Approximately a decade old, yet newer than AVI, the MPEG format was an attempt to provide high quality video using smaller file sizes, as invented by the Moving Pictures Expert Group. The MPEG format has seen several variations over the years, having been one of the first streaming formats using SGI WebForce MediaBase (which failed), becoming the MPEG-1 VCD specification, moving to the digital satellite DBS/DVB/DVB-II MPEG-2 formats, becoming the de facto DVD MPEG-2 format, using the popular MPEG-Layer III (MP3) audio format, and most recently as the MPEG-4 DivX video format for video swapping online.

Compression method. JPEG, MJPEG and MPEG are similar, but please do not confuse them. A JPEG image file groups similar information in the image, and squeezes it into the same space, compressing the file size (for example, in layman's terms, instead of writing "BLUE" 81 times in a row, the compression scheme writes "BLUEx81"). A Motion JPEG, known as MJPEG, does the same, at a frame-by-frame level, essentially a back-to-back series of JPEG images. Each frame is analyzed for similarities, compressed, then the process is started over at the next frame (intra-frame compression). MPEG does this, as well as incorporates temporal compression using groups of pictures (the GOP, made of I, P and B pictures). Information is not only compressed in the frame (intra-frame), but between frames as well (inter-frame, I-P-B). 

Editing. MPEG is a final product video format. After a video has been converted to MPEG, it usually should not be edited, especially ones that follow the full I-P-B compression scheme. There are actually several professional MPEG editing formats, though they use low or no inter-frame compression. For example, an MPEG-2 with I-frames only with CBR encoding, which is almost the same as an MJPEG.

D-Values. Various resolutions are often referred to as D-values. Full D1 video is 720x480. Cropped D1 is 704x480. Half D1 video is 352x480. Quarter D1 (actually SIF) video is 352x240. Two-Thirds D1 video is 480x480. DVB and DVD-VR use unusual MPEG resolutions, sometimes called Three-Fourths D1 at 544x480.

MPEG formats. MPEG-1 is the oldest version of MPEG. MPEG-2 is the updated version of MPEG-1, introducing interlacing, and giving control over more advanced features of the format. DVD-Video uses MPEG-1 and MPEG-2. CD based formats, such as VCD and SVCD/CVD, use either MPEG-1 or MPEG-2 depending on the specs. MPEG-4 is the name given to newer AVIi codecs such as XVID, and is really not the same. See the charts on the UNDERSTANDING YOUR SOURCE guide for detailed information on the varying disc formats (DVD, VCD, SVCD, etc).

File extensions. The following file extension are associated with MPEG files:
DAT = MPEG1 with VCD navigation data 
M1V = MPEG1 video 
M2V = MPEG2 video 
MP2 = MPEG Layer II audio. If it contains video, it is misnamed (ATI MMC did this in the old days)
MP3 = MPEG Layer III audio, not muxed with MPEG video
MP4 = MPEG-4 video file (should be in an AVI), misnamed 
MPA = MPEG Layer II audio 
MPV = MPEG1 or MPEG2 video 
MPG = .3 extension version of MPEG, from DOS/Win16 era, still used Win32/NT 
MPEG = MPEG video, audio or muxed video-audio file 
VOB = MPEG1/2 with DVD navigation data 

AVI captures are better quality? Assuming good capture hardware/software is being used, whether the video is compressed now or later makes no difference. This situation reminds me of the Bugs Bunny cartoon where Daffy asks Elmer, "Would you like to shoot me now, or wait until you get home?" Seriously, there is no difference. Daffy was somehow fooled into believing one was better than the other, yet the outcome was the same. He had his bill blown off.


What MPEG Bitrate?

More is not always better, at least not when the bit-rate surpasses the resolution. Each resolution has an approximate bit-rate maximum, whereas sufficient bits (bandwidth) can be allocated to each pixel. While the MPEG will support bit-rates well into the double-digits, it will likely not use it, and the outcome is simply a bloated file.

352x240/288 = 2.0 MB/s or 2000k max
352x480/576 = 4.0 MB/s or 4000k max
720x480/576 = 8.0 MB/s or 8000k max (same for the 704x480/576 variation) 

MPEG also has an option of VBR (Variable Bit-rate) or CBR (Constant Bit-rate). The VBR encode only takes the amount of data needed to make the picture look good, and has both maximum and minimum variables to work with. The CBR gives each frame the same amount of bit-rate and forces the picture to use it all, whether it was needed or not, resulting in larger file sizes.

On a rare occasion an extra meg (or an extra 1000k) can help out. That is normally limited to situations where the video has extremely fast action or contains multitudes of minute details. The following bell-curves illustrate the quality that can be found with various bit-rates:





How to analyze the graphs: 
- Note the quick rise in quality with small jumps in bit-rate. 
- At a certain point, you'll reach a plateau of quality. 
- The suggested max bit-rates are the earliest point at which this plateau is met in most situations. 
- The next number in the middle of the plateau represents a second safety marker, needed only when extreme aspects of the video require larger bit-rates. This can happen with high action or with high detail. WWE Wrestlemania is a perfect example of program that needs higher-than-normal bit-rates, due to fast action and very detailed crowds.
- The two numbers on the curve, found just prior to the suggested bit-rate (2000,4000,8000), are bit-rates that can often provide excellent quality, though some of that is dependent on the encoder software and the hardware being used.
- The number on the middle of the curve provide barely-watchable quality. Note that VCD falls in this range. These are often full of macroblocks.
- The number on the bottom of the bell curve is the last bit-rate that can be safely viewed (though still a miserable viewing experience). Numbers between it and zero will often be so full of artifacts that the image is lost.
- These bit-rates are not VBR/CBR specific. Using VBR may gain slightly better results. Using CBR may yield slightly lower quality results.

NOTE! 
It appears the people over at mediachance.com really like this information. Shortly after these charts and this article appeared on digitalFAQ.com, it magically appeared on their site with uncanny similarity in both the numbers and the non-tech terms being used to describe it. In fact, the only real difference is they made theirs have pretty colors and crammed it into the same graph. Plagiarism is alive and well, folks! Not even a thank you or a link of reference from them! I guess they're still mad I hate their overly-complex bug-ridden DVD-Lab software, instead preferring the ease and quality of Tsunami DVD Author, DVDit! PE or Ulead DVD Workshop. 


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