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SDI support


SDI support

By October 12th, 2011 Uncategorized No Comments

One of the most requested features for the MobileBroadcast Client is support for SDI devices. For now, the software only supports capturing via FireWire.

Good news: SDI support is coming along! A new version of the client software will be released within the next weeks, which also supports capturing using the Blackmagic SDK, and thus all devices supported by this SDK. For notebooks, the UltraStudio SDI would be of special interest. If you are using a desktop PC for transmitting, the whole Decklink series will work.

But there are also some drawbacks using SDI: The client software consequently adheres to the concept of caching unprocessed data. If the computer’s CPU is to slow to encode video in real-time, the stream coming from the camera is cached on the hard-drive and encoded with a delay.

Instead of transcoding the stream directly, the incoming DV/HDV data are written to the hard drive, and at the same time read from the hard drive and encoded to H.264. The encoding thus went completely independent from capturing, and even slow CPUs wouldn’t cause a single frame drop. This was easy to achieve with DV or HDV captured via FireWire, because they have a data rate of only about 25MBit/s, which is not a problem for modern hard-drives, not even when writing and reading concurrently.

The situation is quite different with SDI: It delivers uncompressed video, which has already 270Mbit/s for SD and usually around 1.5Gbit/s for HD. Even for modern hard-drives, this is far too much for reading and writing concurrently, and thus captured data cannot be cached anymore. It has to be encoded directly to H.264, and the encoded data have to be cached afterwards.

The result is that you will have unrecoverable frame drops if your CPU is too slow to encode in real-time. When using SDI, an automatic “store-and-forward” delivery is only possible with very recent and fast laptop computers.

So as a conclusion, SDI will work well, but make sure to use one of the latest Core i7-2 processors with at least four cores! Slower computers will definitely cause frame drops.