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  #1 (permalink)  
Old Wednesday, July 27th, 2011, 11:04 PM
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SDI video, how about audio?

Hi all,

From what I've read in the forums, SDI is the way to go for video distribution, if you're looking for quality, reliability and simplicity.

How about audio distribution? I've read some things on SDI, that it is able to carry embedded audio. What does that mean?

Eg. If I had a camera video source that outputted to SDI, and an audio source from the mixer that outputted probably quarter inch, could I combine the two sources and output them into one SDI cable?

Also, if I am able to combine the 2 sources, and output to one SDI cable, if I then connect the SDI to a HDMI distributer (1-10), would the HDMI be able to receive the audio and video from the SDI, and output both still?

Thanks!
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Old Thursday, July 28th, 2011, 04:36 AM
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SDI can carry up to 16 channels of audio along with the video signal. To combine audio from your board with video from your camera, you would need to add an audio embedder.

To convert your SDI A/V signal to HDMI, you would use an SDI-to-HDMI converter. Typically, this would convert audio channels 1 & 2 to stereo on the HDMI output, but you may even find more robust converters that would support 5.1 or even 7.1 surround sound.

You would then run a short HDMI cable to your 1:10 HDMI distribution hub.

Alternatively, (and this is how we run,) you could run your video into a computer that has a SDI capture card for direct-to-disk recording. (We use an 8-core Mac Pro with a blackMagic HD capture card.) You also run a feed from your audio board into the capture card's XLR inputs. The capture card does the job of embedding the audio and converting the combined A/V to HDMI. Then you run HDMI out of the capture card to your 1:10 distribution hub.
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Old Thursday, July 28th, 2011, 04:47 AM
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Quote:
Originally Posted by kennefu View Post
How about audio distribution? I've read some things on SDI, that it is able to carry embedded audio. What does that mean?
Standard definition Serial digital interface (or SDI) is just a transport for digital video based on (typically, but not necessarily) 270 Mbps (megabits per second) typically using a BNC connector. Color encoding is 4:2:2 YCbCr . This 270 Mbps pipe is actually capable of moving more than pictures … so you can also have up to sixteen audio channels (8 stereo pairs) of embedded digital 48 kHz, 24-bit audio channels. This audio gets married to the video, called “embedded.” If you want to separate the audio at some point you would need to “de-embed” the audio.

Quote:
Originally Posted by kennefu View Post
If I had a camera video source that outputted to SDI, and an audio source from the mixer that outputted probably quarter inch, could I combine the two sources and output them into one SDI cable?
Yes. You can run audio into the mic inputs on the camera in which case the camera will most likely embedded the single stereo pair into the video signal for you … no other hardware needed … or you can buy a stand-alone audio embedder.

Quote:
Originally Posted by kennefu View Post
if I am able to combine the 2 sources, and output to one SDI cable, if I then connect the SDI to a HDMI distributer (1-10), would the HDMI be able to receive the audio and video from the SDI, and output both still?Thanks!
I am not sure about the SDI to HDMI conversion and audio capability at that point.
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Old Thursday, July 28th, 2011, 05:18 AM
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Quote:
Originally Posted by tdangelo View Post
You can run audio into the mic inputs on the camera in which case the camera will most likely embedded the single stereo pair into the video signal for you … no other hardware needed …
LOL! Thanks, Tom! I should have thought about that first, since that's how we ran for the first year until we got our Mac Pro set up with our capture card.
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Old Thursday, July 28th, 2011, 12:10 PM
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I should add that using a camera as an embedder assumes that the camera has a SDI output.
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Old Friday, July 29th, 2011, 02:48 AM
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Hey guys. Thanks so much more replying. I really feel blessed.

SDI seems brilliant. One simple cable that does it all. But is that really all you guys use for audio distribution? Or do you usually pull an additional audio cable?

Also does anyone know anything about Blackmagic's Videohubs? I want to use it as a on the fly switch. I was wondering if their control software includes effects like cross-dissolves when you make the switches.

Here's a flowchart of what I've put together. Does it make sense? Would love feedback.

SPAVDistribution.png
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Old Friday, July 29th, 2011, 05:05 AM
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BM's video hub is an awesome product (we have one spec'ed for our next upgrade), but it's a purpose-built distribution matrix -- not a switcher. As such, it does not contain the multiple synchronized frame buffers that would be necessary for the advanced video processing necessary for effects like wipes and cross-dissolves.
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Old Friday, July 29th, 2011, 07:48 AM
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Quote:
Originally Posted by kennefu View Post
SDI seems brilliant. One simple cable that does it all. But is that really all you guys use for audio distribution? Or do you usually pull an additional audio cable?
Between pieces of video equipment (recorders, etc.) which support embedded audio, embedded audio is a very convenient way of moving pictures & sound with a locked lip-sync relationship assuming you do not wish to adjust the audio at the destination.

Any type of adjustment or connectivity to most audio devices will require the audio to be de-embedded. Embedders/De-embedders are pricey .. so you should look at the cost advantage / disadvantage of moving audio around this way.

In general, If I were building a new facility I would pull HD-SDI rated video copper (BNC), and one or more types of audio including analog rated audio copper (XLR), AES rated audio copper (XLR), MADI (BNC) & CAT-5.

Thinking long-term I would pull single-mode fiber.
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Old Friday, July 29th, 2011, 11:48 AM
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Quote:
Originally Posted by tdangelo View Post
In general, If I were building a new facility I would pull HD-SDI rated video copper (BNC), and one or more types of audio including analog rated audio copper (XLR), AES rated audio copper (XLR), MADI (BNC) & CAT-5.

Thinking long-term I would pull single-mode fiber.
I agree but would note that one can use the same cable for both AES and analog audio and also the same cable for both HD-SDI and MADI. There may be some minimal cost difference in the cable itself but if you can run fewer cables, not have to deal with multiple cable types during installation and perhaps have greater long term flexibility, that often more than offsets any initial difference in the cost per foot of the cable.

I should also note that I am running into more requests and/or requirements for shielded STP CAT5E/CAT6 and discussions of CAT7 for media use, especially in reference to HDBaseT and AVB. I used to recommend CAT5 for use with AV extenders and baluns but am having to revise that recommendation toward shielded CAT6 in many cases.
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Old Saturday, July 30th, 2011, 05:09 AM
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I think your flowchart looks very serious. You will indeed be preperred to include video production. Maybe latency could become an issue, with all the converters, and probably also a delay thru the videohub.
One thing to be aware of when using the BM HDMI-SDI converters, is that they do not support 1080p.
We are using the BM broadcast videohub, with a 24" touchscreen. It works perfect.
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Old Saturday, July 30th, 2011, 09:17 AM
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Quote:
Originally Posted by Borggren View Post
One thing to be aware of when using the BM HDMI-SDI converters, is that they do not support 1080p.
Really? Based on the spec sheet they support 1080p.

Quote:
Originally Posted by Borggren View Post
We are using the BM broadcast videohub, with a 24" touchscreen. It works perfect.
So what happens when you make a switch during the broadcast. Is it just a hard cut that happens? Is it clean instant cut, or does it flicker a bit before it changes?
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Old Saturday, July 30th, 2011, 10:18 AM
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This is the HDMI formats supported by BM: 625/25 PAL, 525/29.97 NTSC, 625/50p PAL, 525/59.94p NTSC, 1080p23.98/24, 1080i50, 1080i59.94/60, 720p50 and 720p59.94/60.

We are not doing live switching on the Broadcast video hub. Just using it for routing signals. If you want to do seamless switching between sources, you need a switcher for that.
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