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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The next class of devices are video cards with the ability to digitize video. These devices are built around the same video digitizing chips as standalone TV tuners. Video cards with the ability to digitize video are produced by all kinds of video card manufacturers (nVidia, ATI). Among these video cards there are two big classes: with a TV receiver (e.g. ATI All-in-Wonder line) and without a TV receiver (e.g. ATI VIVO line – video in, video out). You can read more about different video cards with video capturing and digitizing functions (including those with TV receivers) in the corresponding section.

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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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You don’t need a powerful processor for capturing video without compression, on the other hand the amount of recorded data in this case will be huge. On-the-fly video compression during capture requires a processor of at least 500 MHz, preferably 900 MHz. The faster the processor you have, the more complex video compression you can apply on the fly – directly during digitizing.

Further video processing will be faster the faster your processor is. Since the task of video processing is purely computational, the speed of the processor is what determines how fast it can go: the amount of memory, how fast your hard drive, and other components all have a much smaller effect. Modern MPEG-4 encoders do not support HyperThreading (see video encoding speed comparison between different processors).

RAM

Video capturing does not require much memory: it is enough for your operating system to feel comfortable and have enough memory for the video capture program and the video compression codec on the fly – about 40 MB for compact utilities. Thus, the minimum can be considered 64 MB of RAM for Windows 98 and ME, 96 for Windows 2000 and 128 for Windows XP. If you are planning to perform some other tasks while digitizing videos, you will need more memory to run your programs. It is not desirable for the system to stop to access the swap file: in this case it might not be possible to continuously record the data stream from the capture card, so it is recommended to have a dedicated hard drive for video (see below).

Hard Drive

When digitizing and capturing video at 768×576 pixels without compression, a data stream of about 22 MB/sec (76 GB/hour) comes from the video digitizing card. Obviously, in order to write such a data stream to a hard disk, you need firstly a lot of free space, and secondly a hard disk with sufficient write speed. Various on-the-fly video compression methods reduce this stream, but additionally load the processor and may degrade the quality of the material. In practice, a compromise with slight compression is used: all the same, less data has to be recorded, and the image quality is reduced slightly (sometimes the difference is not even noticeable to the eye). So, to capture video you need a large hard drive which can record at a high speed.Selecting and connecting the hard drive

It is important that a separate hard disk (IDE or Serial ATA) is used for capturing – the operating system must be on a different hard disk, because it needs to occasionally read or write some data to “its” hard disk: if this disk is busy recording the digitized video, it may just not have time to record the incoming data stream. It is also important that the system hard disk and the video disk must be on different IDE channels: two IDE devices on the same channel cannot work simultaneously. If you have other hard drives, CD or DVD drives and want to use them while digitizing video, an optimal solution is to buy an extra IDE controller (about $15) and connect your video capture hard drive to a separate IDE channel. Stable recording speed of 25 Mbytes/sec over all disk’s surface can be provided by relatively new hard disks, relatively speaking about models produced starting from the second half of 2002.

Hard disk cache capacity is of no importance for video capturing: 2 MB or 8 MB, it records much bigger amount of information per second anyway.

Hard drive for video capture must be connected in Ultra DMA mode.

Hard disk speed also affects video processing speed. However, during normal video noise removal process the video processing speed is very low, just a few frames per second: any hard drive can easily handle that kind of workload. Hard disk read speed becomes a limiting factor only when processing video which doesn’t require complex calculations, e.g. saving audio track to a separate file. The source file after capturing video can be tens of gigabytes long, the whole file must be read to extract the audio – it turns out that in such tasks the speed of a hard drive becomes the determining factor. File System

When digitizing video, you have to deal with files of tens of gigabytes in size. The FAT32 file system is not suitable for capturing video, as it has a file size limit of 4 GB. Some programs support working with so called segmented video – a video recording is divided into several numbered files. However, the process of closing one file, creating a new one, and transferring data stream recording to a new file while capturing video creates an additional load: dropped frames, audio and video mismatching often occur at the file junction. Also Windows does not allow you to create partitions with FAT32 file system larger than 32 GB (although special programs can create a partition of larger size). There is also a popular opinion that the FAT32 file system is faster than NTFS: in fact it is, but the speed gain is insignificant, only 1-2%.

All these problems can be avoided by using the NTFS file system: Windows versions from 2000 onwards support it. Moreover, NTFS has a number of additional advantages in handling a large number of files and large data streams. Thus, if you use NTFS you get a comfortable opportunity to work with big files and easily perform various tasks during the digitization of video (including work with the hard drive where the digitized video is stored).Special hardware solutions

There is a common misconception that working with video requires special hardware solutions: RAID controllers, SCSI controllers, SCSI hard drives. Of course, a hardware RAID controller and a pair of hard drives in striped write mode will run faster than a single hard drive. SCSI hard drives are usually faster than IDE hard drives (plus they are much more expensive and require a dedicated SCSI controller). However, the speed of a modern IDE hard drive is quite sufficient to write a stream of digitized video data.

Operating System

The platform is
I have to admit that I haven’t looked into this question specifically, but I have only heard of one Linux program that works with a video capture card and a TV receiver. I don’t really remember if it allows you to watch TV broadcasts or if you can use it to capture video too. In any case just one program – even if there are a couple or three of them – doesn’t compare with the abundance of programs on the Windows platform.

The second argument: the manufacturers of modern capture cards release fully functional drivers only for Windows. The isolated exceptions (e.g. ATI) only confirm the general rule.

Thus, the choice of platform for digitizing video is more than obvious: the most popular and widespread multimedia operating system today: Windows.What Windows to choose?

The modern variety of Windows operating systems consists of two main groups: Windows 98 (second edition) and Windows ME – the so-called Windows 9x; and Windows 2000, Windows XP, Windows 2003. Earlier versions of Windows do not meet today’s requirements for video capture programs and video capture card drivers – they are virtually impossible to use.

The Windows 9x line is built on the old Windows 95 kernel, which does a rather poor job of allocating computing resources. Therefore, working at a computer while capturing video will be fraught with crashes at the slightest opportunity: floppy disk reading, CD reading error, launching a large program. In practice, you should do absolutely nothing while capturing video on a computer running the Windows 9x family of operating systems: capture failures are too likely. Also, the Windows 9x line does not support the new NTFS file system, which causes a number of problems (see File System section). The only advantage of Windows 9x family operating systems: more modest requirements to the computer’s RAM. If you are limited to 64 MB of memory, Windows 9x is your only available choice.

It is highly discouraged to use an operating system from the Windows 9x family for video capture. Whichever of the newer Windows operating systems you choose is totally indifferent from a video capture perspective. The choice is up to you, according to your personal preferences.Additional operating system components

Microsoft has developed a subsystem in Windows to handle multimedia data, including sound and video: it is called DirectX. Many video capture programs run using DirectShow, one part of DirectX. The drivers of many video capture cards support capturing only using DirectShow.

Microsoft is constantly adding and improving DirectX: optimizing the work of existing subsystems, fixes bugs. The latest version of DirectX can always be downloaded from the Microsoft site. The current version at the time of writing: DirectX 9c (the Windows 2000 package includes only version 7 of DirectX, Windows XP version 8).

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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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