hello rajat Let’s use a scenario to illustrate this decision. John has been asked to shoot a wedding at a local house of worship. He’s chosen to use an all-in-one capture and streaming device like NewTek’s TriCaster PRO, as he knows that he will be using three cameras and graphics (such as the names of the different members of the wedding party) and will need to stream the show live to four relatives who were unable to attend. John checks with the church and is told that they have a cable modem with a 2 megabit per second upload speed, and he confirms that each potential guest has broadband on which they’ll watch the ceremony.
Based on that information, John calculates that he can safely send a 400 kilobit per second stream to 4 viewers, if each one is watching the same video format (in the instance of the TriCaster Pro, it would limited to Windows Media). The calculation is 400Kbps x 4 = 1600Kbps, or just over 1.6 megabits per second. This provides adequate bandwidth overhead to compensate for a drop in upload speed, an occasional church worker sending out small emails, or any other programs that might be running on one of the church’s machines. If John finds out that one of the guests requires Real or QuickTime to view the wedding, though, he will have to use one of the four potential streams for that format and may need to hire space on a streaming server for a block of time during the wedding to accommodate the use of a different format or additional viewers.
Other robust live capture and encoding cards include Digital Rapids’ StreamZ line and ViewCast’s Niagara GoStream.
Asynchronous Capture and Delivery
Live capture for later delivery is quite similar to live capture, but with the marked difference that content can be captured at a higher overall bit rate and then compressed after the fact into a smaller bit rate. In fact, if one is using a digital video camera to capture the event, such as one that uses MiniDV or the newer high-definition HDV format, content can be captured directly in the camera as video data and then transferred directly to a computer via USB or FireWire to be further compressed for web delivery. This process is known as transcoding if the content will be converted from one format to another, or transrating if only the bit rate will be changed while the codec remains the same.
For those without access to a digital camera, it is highly recommended to use a capture card directly, rather than recording to analog tape and then transferring to the computer. The reasoning goes back to initial comments in this article: analog tape introduces a significant amount of video noise (and some audio noise) in the recording process, which is eliminated if the computer is used to capture a first-generation digital file.
For those who might also provide nonlinear video editing services, the great news is that a video capture card for your NLE can serve double duty as your streaming video capture card. In fact, many cards on the market for NLE work have the ability to stream live, using computer drivers that come with the card but aren’t utilized by the NLE system. Companies such as Aja make robust breakout boxes that have all the connection types noted above (S-video, component, SDI, balanced audio, unbalanced audio) and can be mounted several yards away from a laptop or small desktop if space is at a premium when it comes to capturing for transcoding.
The major difference between this type of capture and edited on-demand content, which we’ll cover later, is that it’s assumed this capture is fully self-contained and requires no additional editing or graphics. In the scenario above, where John was asked to shoot a wedding video at his local house of worship, this type of capture might be used if the church has no limited DSL or cable Internet service or too many guests who wish to view the cere
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Answered by
raj u
, an ibibo Master,
at
1:57 PM on May 23, 2008
