Digitizing and capturing analog video
Before I continue my story on video digitization software, I’ll mention the way the Windows operating system implements video capturing. Back in the early 1990’s the Windows operating system was equipped with a video subsystem: Video for Windows (abbreviated as VfW or V4W). VfW also exists in the most modern versions of Windows, and is successfully used by a number of programs to this day.

In the late 1990s, Microsoft developed a new, more flexible subsystem for working with video called DirectShow (since version 7 it is part of DirectX). The vast majority of new programs use this subsystem (interface) to work with video.

It is important for us that the video digitizing card drivers can only implement capturing through DirectShow – some modern cards have only such drivers. This makes it impossible to use digitizing software that uses the VfW interface to capture video: the Windows subsystem which is responsible for using DirectShow video through the WfV interface (the so-called wrapper) limits frame size to 384×288 pixels. For example, the popular series of digitizing cards based on the Conexant bt878 chip supports digitizing only via DirectShow (to be fair I should note that there is a version of the drivers which implements the ability to capture a full frame via VfW: from Eduardo José Tagle).

It should be understood that the task of both subsystems is not limited to video capture only. Each of the subsystems is designed to support the full range of video tasks: capturing, recording, playback, copying, editing. We will be interested in the interface used in the context of video capture – is there support from the capture card driver, is any program able to use this interface to capture video? At the same time, the same program can use another interface for other tasks, for example: writing video to a file.Problems when capturing video

Since digitizing and capturing video takes place at the playback speed of the original video, it is important that the computer has time to process and record the data in time. Possible reasons why your computer can fail: low hard disk recording speed, low processor power when using software compression (the compression algorithm selected has no time to compress a frame in 40 ms), computer resources are “wasted” on additional tasks during capture (e.g. switching the file into which the capture is performed), system tasks (e.g. working with the swap file) or any user programs. Beforehand you are to prepare your hard disk for video capturing (see: “hard disk preparation – defragmentation”), check if your CPU power is enough to compress video to the format you need with the selected settings (test capture a few minutes of your video). During video capturing it is desirable to refrain from work with other programs which are actively using resources of the computer during the capture (processor, disk subsystem).

If the computer has no time to process the incoming stream of frames, some frames are skipped. The video and audio are digitized by different devices, so skipping video frames will cause loss of synchronization with the audio. 25 skipped frames will lead to 1 second lag of the video and audio, therefore it is not recommended to save recordings with more than 5-10 skipped frames: it is better to capture them again. With a properly configured system it is possible to capture hours of video without missing a single frame.

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Most countries around the world have adopted one of the broadcast television standards: NTSC (America and Japan), PAL (Europe), or SECAM (France and the former USSR). Each country sells video equipment that is capable of working with the television standard accepted in that country. If you are using equipment purchased in another country, be sure to check in the documentation of your equipment that your video source and capture card are capable of working in the same television standard.

There are also subtypes of TV standards such as PAL-B, PAL-D, PAL-G and so on. They differ not by the way the signal is encoded, but by its parameters (frequencies and widths of sub-bands). Capture cards are usually able to work with any subtype of the standard, it is only necessary to specify it when setting up the card: either the name of the standard subtype proper is specified, or the name of the country where this subtype of the standard is adopted for TV broadcasting.

Due to the fact that PAL and SECAM standards are very similar: both transmit 25 frames per second and encode the brightness component of the signal (black and white image) identically, the vast majority of video equipment widespread in our country is able to work with both standards – PAL and SECAM. For the same reason video cameras on our market work in PAL: the market in the former USA is not so big to develop a special SECAM version, and since all our TVs and VCRs support PAL, there’s no need to.

NTSC uses a different way of encoding the video signal, in particular it transmits 30 frames per second (to be more exact, 29.97 – although there are devices which transmit at exactly 30.00 fps). Most of the video equipment we use is not capable of working with NTSC. Often there are two versions of capture cards: for PAL/SECAM and separately for NTSC. Be sure to verify that your capture card is capable of working with your video source.

Low frequency blocks of all capture cards are universal and can digitize video signal of any standard delivered to the video input: you just need to set the correct frame rate (25 or 30 for NTSC). High-frequency blocks – TV receivers, on the contrary, are specific for every TV standard. So your capture card will only be able to record video from TV broadcasts in the standard (one or more) for which it is designed. We sell capture cards with PAL-D/SECAM-D standard, which is accepted in former USSR countries.

You don’t have to worry if you use a digital video source: a digital camera will do everything for you. The only difference is that video digitized from an NTSC signal will contain 30 frames per second instead of 25.

In the following text I will assume, for simplicity, that our video signal has 25 frames per second. In case your video has 30 frames per second, you just need to replace the corresponding numbers “25” with “30” and “50” with “60” – the rest of the information is still valid.

For more information, see other articles such as Television Standards: Descriptions, Characteristics.

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The situation changed dramatically 6-7 years ago with the widespread adoption of Pentium generation processors. This processor is enough to play audio compressed in mp3 (MPEG-1 Layer 3) format which allows to achieve good sound quality at 1 Mbyte/min and almost ideal sound quality at twice as much (compare with 10 Mbyte/min on an audio CD). Hard disks at that time were already measured in units of gigabytes. Thus began the ubiquity of mp3 and its alternatives, which continues to this day. A modern computer spends about 1-2% of its processing power to decode mp3: since that time the power of processors has increased by two orders of magnitude.

Around the same time, digital video was taking its first steps on personal computers. Because of the aforementioned limitations on the amount of information processed and processor power, the video of that time looked awful: the “dance of squares” attracted only computer enthusiasts. Again the situation changed dramatically when the computer hardware reached a certain level. By the time computers had reached the 10 gigabyte limit, CD-R burners had become ubiquitous, and processors were approaching the 500 MHz limit, with MMX, 3DNow, and SSE multimedia instructions, computers had reached the MPEG-4 video compression standard. Previous versions of the MPEG video compression standard had significantly less potential for use on PCs.

For example, MPEG-1 offers relatively low video and audio compression, and its implementation in the Video CD standard offered picture resolution of up to 352 by 288 pixels (which is obviously very low for high quality video) and allowed only about an hour of video to be burned onto a single CD. Its advantages included the relative computational simplicity of decoding, respectively low computer requirements (133 MHz). Video CDs have not gained popularity among publishers of video products (movies, etc.). However, the use of cheap CDs as a carrier, and full support by absolutely all hardware home VCD / DVD players have made this format very popular for recording home video. However, the recording quality is very poor.

The MPEG-2 standard offers slightly more advanced compression, and its most common implementation in the DVD standard provides resolutions up to 720 by 576 and allows recording of up to 3-4 hours of video per disc. The problem is that the disc is not a normal CD, but a DVD. Correspondingly more capacious, but also more expensive, less common and requiring additional hardware (DVD-drive). Even the low processor power requirements (266 MHz) didn’t save: the size of a 2-layer DVD is 8.5 Gbytes, which made it impossible to copy them in the era of hard drives up to 10 Gbytes. Video DVDs became the industry standard for recording home videos: movies, concerts, etc. We only see the rise of DVDs as a medium for home video, today, when the capacity of hard drives is over 100 GB, DVD-reading drives are not much more expensive than CDs, burnable DVDs are becoming more and more popular. The same video compression format is widely used in digital television broadcasting, including satellite television.

It was also developed an intermediate format between VCD and video DVD: Super Video CD, SVCD (using CD as a carrier and MPEG-2 as a video compression format, the resolution – 480 × 576, allows you to record about 70 minutes per disc) – its compression quality for the amateur video is enough. The main problem of SVCD is compatibility, not all hardware players are capable of playing discs in this format.

The video compression standard MPEG-4 (or more precisely its “MPEG-4 video compression, advanced simple profile”) was a perfect compromise between the degree of compression (size of compressed video) and the computational complexity of video decoding (processor power requirements). For video playback a CPU of 300-400 MHz is enough (or more, depending on video resolution), and good quality is ensured for 2-2,5 hours compression per CD (or excellent quality for 1 hour compression per CD).

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In a sense the material of this article repeats the FAQ on digitizing video at minimal cost, with the correction that the methods described here provide higher quality video and use newer software and hardware. The article also covers a wider range of questions readers may have.

I’ll point out a few articles that describe more expensive options for digitizing and capturing video: Digital Video Archive for Home and FAQ on Creating and Editing Digital Video. They describe a technique using capture cards with hardware video compression and storing the digitized video in MPEG-2, DV or MJPEG format (this allows you to record only 15-20 minutes of video on one CD, so the preferred storage option for digitized video in these cases is recordable DVD). This method is most fully described on M. Afanasenkov’s website. The other extreme – preparing the recordings for compression to relatively low quality VCD/SVCD formats – is described in the article How and From What to Make a VCD/SVCD. The TV & FM tuners site contains descriptions of many models of capture cards and different programs which are used to watch TV programs, listen to the radio, capture video, control your computer with the remote control. The author of the site is constantly monitoring news in the world of TV tapping and video digitizing cards, including the appearance of new models of devices and new versions of programs. The level of presentation on digitization technology leaves much to be desired and loses significantly to the Observatory. On the other hand, if you found this article too complicated – read the articles on the TV & FM tuners website: everything there is simpler and more primitive.

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