Next LDSTech Broadcast: Digital Media into Meetinghouses

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markjmiller
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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby markjmiller » Tue Jan 15, 2013 7:04 am

PS - I know this setup is currently complicated, but once it's setup it would require little to no maintenance. Eventually, parts of it could be taken over by the church - like hosting RSS feeds by topic & language. Also, the setup could be reduced as well simply by providing pre-imaged SD cards (SD cards act as the system drive for the devices) or at a minimum the ISO images.

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johnshaw
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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby johnshaw » Tue Jan 15, 2013 10:08 am

This is a great idea and very resourceful, it parallels a proposal I put out there mid-last year using Torrent RSS feeds to keep content updated in each meetinghouse. (I'm using Dropbox now, but it requires manual intervention). We'd also need to modify the scraping to scrape from the Media Library from lds.org resources the Church has rather than limit ourselves to the Mormon Channel. A starter image would be good so you don't have to catch up on the 60GB worth of data to download.

Does the RaspPI client support RCA connections as well as hdmi?

As long as the media server is running DLNA and bonjour services for auto-discovery --> there are clients on all the major platforms now that support dlna for free... the program Skifta has just released on the IOS platform and is free -> connecting to my PlexApp Media server very nicely.
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johnshaw
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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby johnshaw » Tue Jan 15, 2013 10:12 am

If it could also do ipad printing, now we're talkin!!!
“A long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom.”

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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby genman » Tue Jan 15, 2013 10:32 am

rmrichesjr wrote:If it's a pure caching proxy, then there are almost no management/administrative challenges... to paraphrase Brother Joseph, let the caching proxy govern itself.... user access would be transparent. When a user tries to access an URL that is cached, the proxy simply serves that URL's content from local cache. If the content is not local, then the proxy downloads it from the central servers and stores it for next time.

Sounds great! Something that does not require a lot of care and feeding by an administrator.

russellhltn wrote:My consern about a proxy server is that the content won't be there the first time it's needed.

What do you mean by it won't be there the first time it's needed? The caching process should not mean that the user can't access it the first time, just that it has to get it over the internet the first time. To the user it will be transparent; they won't know or care whether the information came from cache or over the internet. Of course if you have several people accessing new content all at once, that may be slow, but that's the whole point of the cache, to minimize the chance of that happening.

Looking forward to further developments in this area, especially solutions that once setup will govern themselves.

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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby russellhltn » Tue Jan 15, 2013 11:24 am

markjmiller wrote:-one device acts as a file server (ArchLinux ARM distro) with an attached external usb drive for local storage (1.5TB+) of the church media that provides a network share (samba). This is so we didn't have to open shares on clerk computers w/ MLS installed.


Have you tested to see how many simultaneous streams your server can do? I'd be concerned that such a cheap device doesn't have the horsepower for multiple streams (or that the disk drive can't support it) causing poor playback on Sundays.
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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby rmrichesjr » Tue Jan 15, 2013 1:01 pm

russellhltn wrote:Have you tested to see how many simultaneous streams your server can do? I'd be concerned that such a cheap device doesn't have the horsepower for multiple streams (or that the disk drive can't support it) causing poor playback on Sundays.


A few back-of-envelope calculations indicate that something as inexpensive as the Raspbery PI-based server ought to be able to handle several simultaneous streams. Here are the calculations:

At least in the cable TV industy an SD stream is 3.75Mbps, and an HD stream is 15Mbps. Divide by 8 (bits per byte) for 0.47MBps and 1.9MBps, respectively. That's the demand side. The supply side is made of the raw disk drive, the USB link, the compute platform, and the WiFi network. There seems to be consensus in earlier posts that the in-building WiFi network can handle several streams. Here's the rest:

Raw disk drive: Sequential access with an inexpensive "green" raw SATA disk drive I bought a few years ago is 60MBps. A more modern 1.5TB disk drive ought to be faster than that. With readahead provided by the Linux kernel in the server, it would be pretty surprising to not support 20MBps, even with several independent streams. If a spinning platter can't handle several streams, a single SSD of modest size (60-150GB) per building wouldn't be too terribly expensive, and a decent SSD has way more performance than required for several HD streams.

USB link: I have pulled around 20MBps off a USB2 flash key, so USB2 should suffice. If it doesn't, there are probably platforms that support USB3 and/or SATA.

Compute platform: The Raspberry PI has pretty decent specs and ought to be able to at least max out the USB2 link and/or ethernet link. If it can't handle several streams, there are other platforms with significantly higher performance in the US$100-200 range. There's only one server per building, so that should still be fairly affordable.

Based on the above, the back of my envelope indicates the described server should be able to push about 10 HD streams or 40 SD streams, with fallback positions to overcome limitations that might show up in actual stress testing. After reading the first posting about the setup, I was going to post a one-word reply: "Impressive!" I hope this idea can be carried across the finish line. I wish I had time to at least help with it.

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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby russellhltn » Tue Jan 15, 2013 1:44 pm

rmrichesjr wrote:At least in the cable TV industy an SD stream is 3.75Mbps, and an HD stream is 15Mbps.


Ouch. 802.11b tops out at 11Mbps (not MBps). And IIRC, if a single device calls for "b", then at least a "g" if not a "n" system will fall back to "b". Portable "B" devices should be fairly rare (as long as no one is using salvaged laptops), but I have to wonder if someone's phone might call for "b" if it finds itself in the fringe. I think this needs to be looked into further before supporting streaming over WiFi. (Although maybe a better starting point is to look at the actual rate for the files in question as it may not approach those cable TV standards.)

rmrichesjr wrote:Based on the above, the back of my envelope indicates the described server should be able to push about 10 HD streams or 40 SD streams, with fallback positions to overcome limitations that might show up in actual stress testing.


How hard would it be to create a "fallback"? I thought we were simply downloading files. Or is this a true streaming server that can switch stream mid-flight?


rmrichesjr wrote:After reading the first posting about the setup, I was going to post a one-word reply: "Impressive!" I hope this idea can be carried across the finish line. I wish I had time to at least help with it.


I hear that. This sounds like something I could sink my teeth into - if I had time. But I've seen too many projects fall apart not because they didn't work, but because they couldn't scale. I'd hate for someone to got to a ton of work only to have it fall apart in Sunday school. That's why I want to raise the question now and suggest that stress testing needs to be a part of development to avoid running into trouble later.
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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby rmrichesjr » Tue Jan 15, 2013 5:25 pm

russellhltn wrote:
rmrichesjr wrote:At least in the cable TV industy an SD stream is 3.75Mbps, and an HD stream is 15Mbps.


Ouch. 802.11b tops out at 11Mbps (not MBps). And IIRC, if a single device calls for "b", then at least a "g" if not a "n" system will fall back to "b". Portable "B" devices should be fairly rare (as long as no one is using salvaged laptops), but I have to wonder if someone's phone might call for "b" if it finds itself in the fringe. I think this needs to be looked into further before supporting streaming over WiFi. (Although maybe a better starting point is to look at the actual rate for the files in question as it may not approach those cable TV standards.)

The low rate of "b" would be a concern. However, the 3.75Mbps and 15Mbps numbers I mentioned were just to get a ballpark figure on what a stream could require. IIRC, standard DVDs are in the neighborhood of 10Mbps. Worst case, if the WiFi system reverted to "b", it could still send approx four SD streams over WiFi and the rest over copper. It might be good to adopt a usage model to plug in to an RJ-45 if one is available and leave the WiFi bandwidth available for those in rooms that don't have an RJ-45.

In any case, I was attempting to answer the question of whether an inexpensive Raspberry-PI system could support multiple simultaneous streams. The capacity of the WiFi system is independent of the cost of the local storage and streaming server.

russellhltn wrote:
rmrichesjr wrote:Based on the above, the back of my envelope indicates the described server should be able to push about 10 HD streams or 40 SD streams, with fallback positions to overcome limitations that might show up in actual stress testing.


How hard would it be to create a "fallback"? I thought we were simply downloading files. Or is this a true streaming server that can switch stream mid-flight?

By "fallback", I intended to mean alternative designs that would have higher capacity at a higher cost. I don't know whether the applicable protocols allow a server to change bitrates mid-flight.

russellhltn wrote:
rmrichesjr wrote:After reading the first posting about the setup, I was going to post a one-word reply: "Impressive!" I hope this idea can be carried across the finish line. I wish I had time to at least help with it.


I hear that. This sounds like something I could sink my teeth into - if I had time. But I've seen too many projects fall apart not because they didn't work, but because they couldn't scale. I'd hate for someone to got to a ton of work only to have it fall apart in Sunday school. That's why I want to raise the question now and suggest that stress testing needs to be a part of development to avoid running into trouble later.

Agreed that stress testing should be part of the development process, ideally including some testing in actual meetinghouses under realistic operating conditions.

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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby russelljd » Tue Jan 15, 2013 6:34 pm

At least in the cable TV industy an SD stream is 3.75Mbps, and an HD stream is 15Mbps.


For all of the content compressed by CHQ for web delivery you should see the 1080p version right around 8 Mbps, 720p version around 2.5 Mbps, and the 360p version around 1.2 Mbps. So your estimates are actually quite conservative.

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Re: Next LDSTech Broadcast: Digital Media into Meetinghouses

Postby rmrichesjr » Tue Jan 15, 2013 6:47 pm

RussellJD wrote:
At least in the cable TV industy an SD stream is 3.75Mbps, and an HD stream is 15Mbps.


For all of the content compressed by CHQ for web delivery you should see the 1080p version right around 8 Mbps, 720p version around 2.5 Mbps, and the 360p version around 1.2 Mbps. So your estimates are actually quite conservative.


Thanks for those numbers. Knowing those numbers apply to all such content is even better than if someone had measured a few and extrapolated. Also, independent of the server platform, those numbers indicate even "b" WiFi should be able to handle several 360p streams or a few 720p streams, assuming the WiFi protocols are reasonably efficient in such cases.


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