DV

DV25 Capture Rate = 3.6MB/sec = 216 MB/min 2 GB for every 9.5 minutes of video

*** pay special attention to when I am talking b (bits) and B (bytes) – computer stored data is usually referred to in Bytes and data rates are referred to in both bps and Bps

Standard, non-DV AVI files do not have Type1 and Type2 designations. Therefore whenever you hear of Type1 or Type2, it refers to DV AVI files.

OpenDML is a common Type2 DV AVI codec. Unlike standard AVI files, which have a limit of 2 GB, OpenDML DV AVI files have no file size limit. However, they are limited to what the file system will allow. FAT32 limits file sizes to 4 GB, while NTFS has no file size limitation (actually there is a limit but it is in the unreachable Terabytes range).

This is the native DV interleaved stream that is produced and consumed in I/O with a DV device. It contains DV compressed video and pulse code modulated (PCM) audio data. This single interleaved stream can be stored in an AVI file as "ivas" stream (for interleaved video/audio stream). Microsoft refers to this format as a type-1 DV AVI file.

Because the type-1 format stores data as a single AVI stream, type-1 DV AVI files are not compatible with VfW. DirectShow, however, easily handles type-1 data streams by routing the streams to a DV Splitter filter that produces a DV-encoded video stream and one or more PCM audio streams for playback or subsequent processing.

Interleaved DV data can also be split into a single video stream and one to four audio streams within an AVI file. Microsoft refers to this format of storing DV data as type-2. This format has the advantage of being backward compatible with VfW, because it contains a standard video "vids" stream and at least one standard audio "auds" stream.

Notice that the type-2 file format requires a small amount of additional processing to split and multiplex the DV stream during the functions of capture and transmit to IEEE 1394 DV devices

DV Video is filmed with a 4:3 lens but is placed into 720x480 (3:2) frames by using oval pixels with an aspect ratio of 0.9. So the 720x480, obviously is not 4:3. When you view it on your computer is appear squashed down vertically and stretched horizontally - unless your software compensates by using the DV1 ratio of 0.9 in reverse.

On your TV it looks fine because the TV compensates for this in two ways . . . by using rectangular pixels and by cropping pixels off the sides – the result is that the 720x480 pixels on the DV tape, when sent to TV, are displayed at 4:3.

Summary - a full-resolution DV image displayed on a computer monitor when using square pixels looks strangely short and wide -- circles become ovals -- but the same signal routed out to a television looks fine. Alternatively, a 720x480 DV signal can be resized to 640x480 for display on a computer monitor to add height and make it look OK, but will then look too tall on the TV screen. DV is meant to be shown in it’s final form on a Television, so leave it as is, at 720x480.

Video Horizontal Resolution in Lines vs PC’s resolution in Pixels (using width/height) - horizontal lines of resolution refers to the number of horizontal lines, which is the same as the vertical size !!!!!!!!!! Vertical resolution of a PC refers to the vertical dimension in pixels, which is the same as the numer of horizontal lines. So horizontal resolution of DV video CANNOT BE COMPARED to the width (i.e. horizontal length in pixels) of the video on your PC. Compare it instead to the height (i.e. vertical length in pixels) of the video clip in your PC.

NOTE: many people believe that the advertised 500 lines of horizontal resolution does refer to width and that the DV width of 720 pixels is multiplied by something called the “Kell factor” of 0.7 to get 500. I still believe it means height, but here is some info from the web that indicates it means width:

The 720 pixels of a DV 'scan line' are turned into a waveform to fill the time of the video scan line (~ 50 microseconds). You'll note that DV advertises '500 lines of horizontal resolution...' this is actually inaccurate: there are 720 pixels in a horizontal line; to get the resolution per picture height, multiply that number by 3/4; you get 540; this is the resolution in horizontal pixels per picture height; to convert this to resolution in horizontal lines per picture height, multiply by the Kell factor, which is usually taken to be ~ 0.7; therefore the actual video resolution per picture height of DV is actually about 380 lines. They advertise '500 line' resolution because they don't standardize it to 'per picture height;' 720 x 0.7 = ~500 lines... this actually means 500 lines across the entire width of the picture.

Interlaced Video - video uses interlacing. 2 fields = 1 frame. The fields are both components of the same frame which is filmed at one exact instant in time - even though one field is scanned onto the screen “after” the first field in time. So the fields are sent to the screen 1/60 ^th of a second apart – but they represent the same exact instance in time – when the frame is filmed !!!

So both fields are from an identical source, but ore off by one horizontal . The horizontal lines of resolution on a monitor or TV screen is defined by the frame – not the fields !! Therefore the number of lines constituting 1 frame should ideally be equal to the number of horizontal lines of resolution.

Resolution of Television - a standard television screen uses 525 lines for the fields, and about 45 are retrace lines - which gives you about 480 lines (the exact number is 486 “active” lines) for the fields but 6 are cropped – or 240 horizontal lines of resolution (each frame is comprised of 240 lines where each line = 2 fields). This is why a small, 320x240 video on your PC can be output to VHS tape and still look fairly clear – the television resolution of 240 is exactly that of the video clip’s resolution of 240 !!! However, the vertical resolution has no such limits, so if you use a 640x480 video clip instead, it will look sharper because the TV can reproduce the 640 pixels going across from left to right.

The TV “fits” whatever it receives into the 480 visible field lines, or 240 horizontal frame lines. VHS output is about 250 lines, which are then sampled to fit into the visible portion of the screen.

Well this is complex. Television “pixels” are not square – they are rectangular: A picture height of 480 has 540 pixels across. Actually it does not use “pixels” but that defines the ratio.

During filming compression occurs in the camera (not the capture) !! The data stored on the miniDV tape is compressed.

During capture, no compression occurs - the data is just piped into the computer, as is, and stored on the hard drive at 3.6 MBps.

Camera compression of audio and control info – None – stored on tape at at 0.5 MBps

These are all compression codec standards. Digital camcorders use one or the other (my Sony TRV900 uses the DV25 codec – it compresses as it films and stores the video to miniDV tape).

For DV25, the camera uses a hardware codec, reducing the data rate by 1/2 through 4:1:1 color sampling and another 5:1 through a low loss compression algorithm. The original 31 MB/sec is thus reduced to 3.1 MBps, which is 25 Mbps – hence the name for this codec process: DV25 (3.1 MB/sec = 25 mb/sec). Audio and control information adds to that, increasing the data rate to around 3.6 MB/sec.

DV25 CODEC – the default compression is 5:1, and it uses 4:1:1 color sampling - the codec capture rate is 25 mb/sec (“bits” per sec) which is the same as 3.125 MB/sec – then you must add audio and control information, which boosts that to 3.6 MB/sec

DV50 Codec – we will not go into detail on this codec. Basically it doubles the data rate of DV25, uses 4:2:2 color sampling, and therefore is cleaner (if your eyes are that good). DV50 is 50Mbps or 6.25MBps per second. DV50 is essentially the same as Digital-S.

DV25 vs DV50 - for broadcast-type applications, what you really want is a flat 400 lines (5MHz), and resolution beyond that mostly adds noise. So for the viewer, DV50 probably will not yield noticeably higher quality video !!

Unlike analog camcorders, the tapes used in digital camcorders consist of a series of 1’s and 0’s. There are several formats, but this paper will only include the Mini-DV tape, which is what my Sony TRV-900 Digital Camcorder uses.

Timecode Problems - it is very important to use "continuous timecode" on all your tapes for Video Capture. Otherwise when the RapVideo rewinds to find the beginning frame, by default it goes past that point and then creeps forward to find the exact frame. If you set an IN point at the beginning of one set of timecode, RapVideo will rewind past that and enter the previous timecode - then it becomes confused and will keep rewinding.

When you put a new tape in and record, it begins one timecode "set". Then when you stop recording it ends that set. Then the next time you begin recording it starts a new timecode at 0 secs.

Also if you can help it - do not remove the tape - that resets the timecode and creates a new set of timecode when you re-insert the tape.

1) the best method - You should "blackstripe" each tape before using it - record nothing from beginning to end to lay down a continuous timecode.

2) If you did not have time to blackstripe, or if you do remove the tape, then reinsert it, and rewind just slightly into the previous recorded set so that the tape will see that timecode and resume recording from there.

To bring the video into your PC you must “capture” it. DV capture requires an IEE 1394 interface, also called “firewire”. Most modern motherboards come with this interface. If your PC does not have one, you can buy a PCI capture card from any number of vendors. Canopus is highly recommended. Pinnacle is not. For a cheaper card, look into Pyro.

The process is simply – you plug the firewire cable into your camcorder, switch it into play mode, and start the capture utility on your PC. You then begin capturing the video at a rate of 3.6MB/sec. 216 MB/min, or 2 GB for every 9.5 minutes of video.

NOTE: if your drive is FAT32 it will max out at 4 GB for AVI files. FAT16 is even worse at 2 GB. NTFS drives have no limit. So you may need to know how much you can capture before reaching the AVI limit :

Even if you are using FAT16, you can capture more than 9 minutes, if your utility supports "reference video”. It will spread the data out across multiple files (capture,avi, capture.001, capture.002, etc). Premiere can open the first file of the series (capture.avi) and will automatically stitch them all together.

AVI I/O supports reference AVI, as does the Canopus capture card utility called RapVideo.

a format backed by manufacturers such as Sony, Philips, Thomson, Hitachi, Matsushita (Panasonic) and others. DV cassettes are designed for maximum performance when used with today's digital video (DV) camcorders and VCRs. As the first digital video recording system for consumers, Mini DV represents a significant advance in video quality over conventional analog recording, with an unprecedented 500-line horizontal resolution-100 lines greater than Hi8 or S-VHS recording.

The DV format has two cassette sizes: Standard/ Full Size (125mm by 78mm by 14.6mm) and Mini DV (66mm by 48mm by 12.2mm). The new DV VCRs will accept both, but the current crop of camcorders accept only the Mini DV.

Mini DV – [my Sony TRV-900 uses Mini DV tapes – the most common are the 60 min (60 min SP and 90 min LP), and 80-min but are also available in 30 and, oddly, 63 minutes. The camcorder allows you to switch between SP and LP. They are manufactured by TDK, Maxell, Sony, Fuji, Panasonic, RCA, and JVC. Mini DV cassettes can also have a small 4K memory chip referred to as memory in cassette (MIC). You can use this to record a contents list, times and dates of recordings and the camera settings used. A label on the tape identifies it as MiniDV, and an odd icon is used to denote memory, as follows (the icon is supposed to be “CM” – Cassette Memory) :

DV tapes with IC Memory Chips (expensive – 20 bucks per tape) allows you to label the tape, or build a "Table of Contents" with dates of the tape that can be accessed automatically to locate a particular recording date, index point or even add titling to the memory that can be turned on and off during playback.

The IC Memory Chip in Mini DV tapes does not effect the way the picture is recorded and is not needed to get great results.

DV cassettes are designed to take full advantage of the DV format, providing remarkably faithful image reproduction with lifelike color and detailed edge sharpness, along with the ability to record digital audio with better than CD-quality stereo sound. DV cassettes feature a considerably smoother surface than other tapes, for improved tape-to-head contact and exceptionally low error rates. Because of this, it is extremely important to keep the recording heads clean. A DV head cleaner is used for this purpose and is highly recommended. DV cassettes are also engineered for peak performance under the most demanding conditions. A specially developed back coating and ultra-high precision cassette mechanism minimize friction and assure the highest degree of tape stability. In addition, the anti-static cassette shell is tightly enclosed to protect the tape from dust and airborne contaminants.

Digital vs. Analog

The Digital Video format offers more precise image detail and color accuracy than previously possible with analog camcorders. The superior quality of digital video results from:

Digital Audio
Quality That’s Crystal Clear

Digital Video (DV) camcorders record audio in the digital format, which gives you the power, clarity and accuracy you’ve become accustomed to from compact discs. The unparalleled sound of DV audio results from:

DVCPRO is a professional variant of the DV by Panasonic. The only major difference is doubled tape speed, which is needed for better drop-out tolerance and general recording robustness. It is also capable of 4x normal speed playback. This doesn't mean ordinary Fast Forward with picture, but rather, accelerated transfer of all of the information, for example, into a non-linear editing system.

DVCam on the other hand, is Sony's variation of the theme, sitting somewhere between DV and DVCPRO. Tape speed and track width have been increased, but not as much as for DVCPRO. Furthermore, it uses the same metal evaporated tape as DV, while DVCPRO uses metal particle tape.

As for the picture quality, all these variants are nearly broadcast quality, DV being available at consumer prices. For news gathering and other similar uses, the quality is certainly enough, especially considering that typical post production will be done digitally, which will not degrade the quality any further.

All mentioned digital formats use the IEEE 1394 digital interface (often called Fire Wire).

The IEEE 1394 interface is a standard serial interface found on most camcorders that allows a connection to other digital equipment. When copying or editing, you will get the best video quality when using this interface, but not all DV Camcorders have an IEEE 1394 Firewire connector.

Introducing the next generation of digital data storage media, the Memory Stick™. Smaller than a stick of chewing gum, it has many times the capacity of a standard 3.5" floppy disk, while providing the ability to interface with and between a potentially endless array of audio/video and computer products.

With Memory Stick digital data storage, you can transfer data, text, and graphics, from one electronics device (e.g. Digital still camera's and digital camcorders) to another (e.g. Laptop or desktop computer or a Memory Stick printer).

Format	BIT RATE	SIGNAL SAMPLING	COMPRESSION RATIO	TAPE WIDTH
DVCPRO	25 Mb/sec	4:1:1	5:1	1/4"
DVCPRO 50	50 Mb/sec	4:2:2	3.3:1	1/4"
DV & Mini DV	25 Mb/sec	4:1:1	5:1	1/4"
DVCAM	25 Mb/sec	4:1:1	5:1	1/4"
DIGITAL-S	50 Mb/sec	4:2:2	3.3:1	1/2"
BETACAM SX	18 Mb/sec	MPEG-2 Inter-Frame	10:1	1/2"
DIGITAL BETACAM	90 Mb/sec	4:2:2	2:1	1/2"

Format	Format Compatibility
DVCPRO	Record DVCPRO, Playback of DV and DVCAM
DVCPRO 50	Some Machines Switchable to Record and Playback DVCPRO
DV & Mini DV	Record DV, Can Be Played Back on DV, DVCAM & DVCPRO
DVCAM	Record DVCAM, Playback of DV, Played Back on DVCPRO
DIGITAL-S	Model Available that Plays Back S-VHS (Analog)
BETACAM SX	Model Available that Plays Back BetaCam SP (Analog)
DIGITAL BETACAM	Model Available that Plays Back BetaCam SP (Analog)