Difference between USB 2.0 and "capture card"

[sjmaye]

OK, so it is a newbie question, but I am kind of confused. On my old computer I bought a generic PCI board that gave me several USB 2.0 ports and a firewire port. I was able to successfully capture video from my DV camcorder with no lost frames (as best I could tell).

I now have a new computer where all the ports on it are USB 2.0 and I was wondering I can capture directly through these or do I need what everyone here calls a "Capture card".

First- What is the difference?
Second- When streaming data from a DV camcorder does it make a difference whther I use a standard USB 2.0 port or from a dedicated capture card?

[Duchess]

USB is a general purpose serial port, like your standard D connector serial port but a hell of a lot faster. It isn't a dedicated purpose port so no, it can't be used for capturing unless a USB capture unit is used that converts video to a suitable format that can be passed via the USB port.

BTW the same applies to firewire.

As regards the DV input most camcorders have a converter built in (usually firewire) so that video can be streamed through the serial port.

[corwin102]

I think the problem is language. You actually transfer your video as data ( like from a flashdrive ) from a DV camcorder so yes you could use your computers built in USB 2 ports if your camera supports USB transfer.

Capture is the conversion of an analog video input signal to digital. This is not necessary for input from a DV camera as the video is already stored on the camera in a digital format.

[gadgetguy]

Your old PCI card had both USB2.0 ports and firewire ports. Which did you use to transfer your video?
As corwin102 stated, if your camcorder supports USB video transfer then you can use one of the USB ports on your new computer. If your camcorder only supports firewire for VIDEO transfer (many have firewire for video, and USB for stills) then you will need to add firewire ports to your new computer. The good news is that you can probably move the old PCI card to your new machine.

[edDV]

If your camcorder only supports firewire for VIDEO transfer (many have firewire for video, and USB for stills) then you will need to add firewire ports to your new computer. The good news is that you can probably move the old PCI card to your new machine.

Consister this the normal case. MiniDV and Digital8 camcorders use firewire (IEEE-1394) for primary interface to the computer. The standardized DV transfer interface includes:

1. Bi-Directional Video and audio streams with video transfer standardized at 25Mb/s.
2. Metadata such as timecode and camera start/stop flags used to define scene changes
3. Device control for the camcorder (e.g. rewind , stop, pause, play, ff, zoom, rec, cue, etc.)

Most MiniDV cameras that include a USB2 interface only support still image transfer and highly compressed streams intended for network (webcam) remote viewing over that port. Some support higher bitrate streams but those are the exception to the rule. The USB2 port is NOT supported by editing applications.

In all cases with a camcorder, audio and video are sent as a stream. There is no concept of a "file transfer". The stream gets transferred to a file at the computer end. Since there is no file, there is no handshake and very limited transfer error correction. That is why care* should be used while transferring MiniDV data since dropout or frameloss can occur.

Bottom Line: Use the firewire port for MiniDV camcorder Video/Audio transfer.


*The total sustained DV data stream including video, audio, metadata, control, and transmission overhead is approx 35Mb/sec. Consider this in comparison to a fast internet connection at 1.5-4.0 Mb/s or a 10BaseT Ethernet connection that can barely maintain 7Mb/s sustained. A DV stream needs to be continuous for hours and represents a subtantial amount of data flow. Minimize or control background tasks while transferring.

[trhouse]

Some USB2 capture devices like the Adaptec Videoh DVD ( model AVC-2200 ) use proprietary drivers. There is limited software that will work with these.

[edDV]

OK, so it is a newbie question, but I am kind of confused. On my old computer I bought a generic PCI board that gave me several USB 2.0 ports and a firewire port. I was able to successfully capture video from my DV camcorder with no lost frames (as best I could tell).

I now have a new computer where all the ports on it are USB 2.0 and I was wondering I can capture directly through these or do I need what everyone here calls a "Capture card".

First- What is the difference?

A capture card is a PCI card (or PC card) that takes analog video in* and outputs digital video data to the PCI bus. Some capture cards also process audio, others include analog and/or digital TV tuners. Simple cards just convert analog video sources to (high rate) digital data. Other more sophisticated cards include hardware encoders (e.g. MPeg2, MPeg1, MPeg4, DV, DivX, WMV, etc.) and output more compact and directly usable data streams thus minimizing CPU processing time.

The functions of a PCI capture card can be packaged into an "external capture device" that connects to the PCI bus through USB2 or IEEE-1394. These range from simple "converters" that export high rate raw digital video, to more sophisticated "hardware encoders" that output more compact directly usable files over the USB2 or IEEE-1394 connection. This type of device is relatively new and is still somewhat risky. The user feedback data is sparse and sorting the good models from the junk is just beginning. Also, expect USB2 models in particular to have limited software support since video transfer and device control over USB2 has not been standardized.

* typcially composite or S-Video (NTSC or PAL) plus analog RF (for tuners)

[sjmaye]

Thanks for all the responses. So, if I get it right, a true "capture card" is used to convert analog video from things like a vcr or analog camcorder.

My USB 2.0 and Firewire port are generic, but have a great enough data rate to stream and receive data from a DV camcorder. This process is not true "capturing". It is merely transferring data from one device to another.

Thanks for clearing that up!

[java-fan.trojanhorse]

Thanks for all the responses. So, if I get it right, a true "capture card" is used to convert analog video from things like a vcr or analog camcorder.

My USB 2.0 and Firewire port are generic, but have a great enough data rate to stream and receive data from a DV camcorder. This process is not true "capturing". It is merely transferring data from one device to another.

Thanks for clearing that up!

------------------------------------------------------------

Not really...

Capture means to convert the RAW material into a new material that PC can use! it doesn't matter if it's digital or analog - it's the same thing ....

Camcorders have gone into digital world. Most consumer digital camcorders use MiniDV format and in order to transmit the data it needs a system that can carry digital signals toward other device which is known as Firewire. MiniDV is just like any other digital video format out there but specifically designed for camcorders in reasons!

MiniDV is a RAW format just like the analog from HI8 or VCR. In order to use these formats in the PC world you have to convert them into another format. This where CAPTURING comes in!

During capture it converts MiniDV(digital) or HI8(analog) into PC format such as AVI,WMV,MOV,MPEG, etc .... to use it for PC applications. So you need a Firewire capture card or Analog capture card ... Is that simple!

Now to USB 2.0 - Some camcorders record their shots into a different format not MiniDV but MPEG. During digitalization process inside the camcorder, the camcorder converts analog signal into MPEG instead of MiniDV(everything starts in ANALOG by the way). Why? MPEG is a FINAL format not a RAW format like MiniDV although they are both digital videos but still they are different. MPEG consumes less space than MiniDV but lower quality though.

Since MPEG is used in PC world that means you don't have to convert it or capture it with another format instead you just TRANSFER it through the use of USB 2.0 - so technically you're not capturing but transfering!

Why not use USB 2.0 for MiniDV instead of Firewire? Firewire is a lot faster than USB 2.0 - You need super fast connection or else you will loose frames during capture. It was first developed for Apple Mac computers which became popular because of it's performance!

[edDV]

Thanks for all the responses. So, if I get it right, a true "capture card" is used to convert analog video from things like a vcr or analog camcorder.

Yes, usually a "capture card" or "external capture device" is used to convert analog video to a digital format. Digital conversion is usually done first to an uncompressed component dataflow in some form of YUV. Simple cards output this uncompressed data flow to the HDD for later processing in software. Other cards include hardware "codecs" (coder-decoder) to convert into other video/audio formats.

A DV camcorder (MiniDV or Digital8) has a b-directional hardware codec built-in (for DV format). The CCD camera output is immediately encoded into DV format. The DV stream can be either passed directly to the IEEE-1394 interface (aka Firewire, Ilink) or recorded to tape for later playback.

The DV codec can also be used as a "capture device". External analog inputs can be realtime encoded to DV format and stored to tape. Some models have a feature called "analog pass through" that allows analog inputs to be realtime encoded and passed directly to the IEEE-1394 interface for recording directly to the computer HDD or used as a realtime stream.

My USB 2.0 and Firewire port are generic, but have a great enough data rate to stream and receive data from a DV camcorder. This process is not true "capturing". It is merely transferring data from one device to another.

Basically yes but IEEE-1394 is highly optimized for DV camcorders (see above) and USB2 isn't. Any USB2 device that supports DV is using proprietary software so expect these devices to have limited support in other applications. DV camcorders don't need an external device. They should just use a IEEE-1394 port on the motherboard or a IEEE-1394 PCI card (or PCcard). When connected properly, IEEE-1394 DV transfers are managed by XP (Directshow, part of DirectX).

To add to the confusion, most applications use the term "capture" generically to include both analog to digital conversion and digital stream transfer. Some in this forum champion a more limited definition of "capture" to mean analog conversion only and "transfer" to mean stream or file transport. Just be aware that outside this forum "capture" includes both.

[edDV]

Not really...

MiniDV is a RAW format just like the analog from HI8 or VCR. In order to use these formats in the PC world you have to convert them into another format. This where CAPTURING comes in!

java-fan.trojanhorse,
There is nothing RAW about DV format. It is a lightly compressed format very similar to MPeg2 and is directly used in editing and authoring software. You may mean that DV is transfered as a data stream and that is true. There is no file until the stream is processed by the computer into a file on the HDD. If a DVD is the goal, DV is "encoded" into MPeg2 prior to DVD authoring.

http://www.adamwilt.com/DV.html
http://www.dvcentral.org/

...
Why not use USB 2.0 for MiniDV instead of Firewire? Firewire is a lot faster than USB 2.0 - You need super fast connection or else you will loose frames during capture. It was first developed for Apple Mac computers which became popular because of it's performance!

IEEE-1394 and USB2 are both general purpose interface standards. When bound into a network under OS control, both can be used for network file transfer. Both can be used for external HDD control.

IEEE-1394 has a second use for DV device interface that is highly and directly supported by XP, Mac OS and Linux. USB2 does not include this feature.

USB2 is mostly used for general device interface (from keyboards to printers). There are few if any high level video transfer or control modes in the USB2 standard. When an application is written to use USB2 for video transfer, specific drivers are written to adapt USB2 to the task. These drivers are generally proprietary to a particular manufacturer and may have very limited software support.