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PostPosted: Wed Oct 27, 2010 12:24 pm 
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Hello Everyone,

A group I am working with has been doing quite a bit of work on hardware and software development in the video encoding and transcoding space over the last year.

We have been working with a hardware based MPEG-2/AVC HD-HD capable encode/transcode chipset for the cable/telco/IPTV market. Recently we have been discussing the possibility of doing some consumer focused products with the chipsets and as a long time Myth user I wanted to poll the group to see what you feel is missing, or could be improved, on the hardware side of things.

I know the HDPVR has been a successful product with the Myth crowd, and I wanted to use that as a jumping off point to ask "what would your ideal encode/transcode box do?"

Some ideas that we've been kicking around are:

-HDPVR style unit that does HD Component capture, but can also do MPEG-2 -> AVC HD/SD transcode and downcsale (so that when not capturing it can be converting existing video from other sources, downscaling HD to SD or mobile formats etc). File based transcoding would happen faster than real time at very low power draw

-Is an ATSC/ClearQAM tuner in such a box desireable?

-Should a unit be USB based or is a stand alone Ethernet setup like the HDHomeRun preferable?

-If the unit were to be stand alone, is it appealing to speak UPnP and be able to host storage and access other network shares?

We're just at the white boarding stage and wanted to see what ideas might bubble up from the community based on real needs and experiences. Nothing is too off the wall, throw it out there and lets see where the discussion goes.

Thanks,

-Jeff


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PostPosted: Wed Oct 27, 2010 1:44 pm 
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Location: middleton wi usa atsc
I would like to see something comparable to the old analog video to RF modulators but for digital TV instead. You know, something that has maybe component video inputs and audio inputs and converts it to RF and outputs to digital channel 3 (or something).

Or maybe something with a USB input and an RF TV channel output. Feed it an already compressed Mpeg-2 stream and get a digital TV channel output.

The already compressed Mpeg-2 stream being one that you have already got on your Myth box from an over-the-air ATSC recording, for instance.

You could then mix the RF channel 3 (or what ever) into your antenna system and watch HD MythTV on any HD TV in the house.


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PostPosted: Wed Oct 27, 2010 1:58 pm 
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Interesting. What you are describing is what the cable industry refers to as an edge QAM. It takes MPEG-2 transport stream and muxes multiple single programs in to a multi-program transport stream and then puts it out over RF.

Let me see if I can paraphrase what you're saying:

You would like the ability to play back mythtv content over clearQAM over the coax within your house?

What are you currently using for MPEG-2 capture?

-Jeff


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PostPosted: Wed Oct 27, 2010 7:51 pm 
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Location: Brisbane, Queensland, Australia
I like jzigmyth's idea, but instead of a digital channel, make the box DLNA compliant. I personally don't use the tuner in my TV, I use my Mythbox via a HDMI and audio to my stereo, I don't even have an aerial point at my TVs.

Ethernet connectivity is always good, I love my HDHomerun as I have it in my server rack, however most people this sort of device is targetted at would not use such a setup.

I have some other ideas that I want to convey although I don't have time at the moment, hopefully I will get to them later and get back to you.

_________________
Girkers


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PostPosted: Wed Oct 27, 2010 7:54 pm 
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DLNA is part of our software stack, so that is easy for us to include.

I'm not sure I am making the connection between the digital channel (or not) and DLNA compliance though. I don't use the tuner in my TV either, I have two cx18's in there that do my free-to-air and then I watch them via Myth over HDMI (is this what you meant as well?).

I'm surprised to hear you say you think most people who use the HDHomeRun wouldn't use it in the way you would. What other way would they use it?

I look forward to your and any other ideas and suggestions. No need to worry about technical viability, more interested in end user experience and can then work back in to viability.

-Jeff


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PostPosted: Wed Oct 27, 2010 8:11 pm 
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Location: Ft. Worth TX
I've converted most of my digital video card mythboxes to HDHR 'cuz it's a superior tuner ...... :D


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PostPosted: Wed Oct 27, 2010 11:11 pm 
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Joined: Wed Mar 07, 2007 9:51 am
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Location: Uniontown, PA
I'll jump in here and say....

ATSC to MPEG2....OR ATSC to DVD-VOB.

Why? It's a standard, and it won't be changing anytime soon, if ever.

I spent most of my time tanscoding OTA broadcasts to the lower formats. I get about 3GB out of an 8-6GB program.

I'm considering blueray for archival...but I wish that HD-DVD was still out there!

Anybody have a HD-DVD burner they want to sell?? ;)

--

Larry


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PostPosted: Thu Oct 28, 2010 12:07 am 
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larrybpsu wrote:
I'll jump in here and say....

ATSC to MPEG2....OR ATSC to DVD-VOB.

Why? It's a standard, and it won't be changing anytime soon, if ever.

I spent most of my time tanscoding OTA broadcasts to the lower formats. I get about 3GB out of an 8-6GB program.



Just to get further clarity, do you mean converting ATSC to MPEG-2 Program Stream? ATSC broadcasts are already in MPEG-2 Transport Stream (TS) format. You shouldn't need to convert them if you want MPEG-2 output, unless you need program stream specifically.

MPEG-2 TS is the standard in the cable/broadcast industry, so it isn't going away any time soon either, but it may not be easy to work with as an end user from a playback perspective.

When you say transcoding the OTA content to the lower formats, do you mean lower resolution or? Would if be valuable to be able to transcode at 2x-10x real time from ATSC MPEG-2 TS HD to MPEG-4 AVC HD?

What settings do you target for archiving that yields 3 GB for an OTA HD? What resolution and bitrate?

Thanks,

-Jeff


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PostPosted: Thu Oct 28, 2010 11:31 am 
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Location: middleton wi usa atsc
jac1d wrote:
Let me see if I can paraphrase what you're saying:

You would like the ability to play back mythtv content over clearQAM over the coax within your house?

What are you currently using for MPEG-2 capture?

-Jeff
I would like to play back mythtv content over UHF ATSC channels through the coax within my house. EDIT: (8-VSB not QAM)

Let me describe what I am currently doing so you can see where I'm coming from.

I have a combined frontend/backend and only do over-the-air recording of ATSC HD channels from an attic mounted antenna. I have three tuners,a dual HDHomeRun and an HD3000. The video card has DVI out and S-Video out connectors. The DVI is adapted to HDMI and feeds the big screen TV in the livingroom. There are many other small TVs through out the house all connected to a common antenna, through coax.

The S-Video out of the Myth box, along with left and right audio, are connected to a video modulator.( http://www.amazon.com/LABS-1001ST-Stere ... B000FR56IE ) set to UHF channel 42. The output of the modulator is combined into the antenna system and adds channel 42 (mythtv content) to all the other over the air channels in the area.

I use IR remote repeaters ( http://www.smarthome.com/8210/Powermid- ... 01-/p.aspx ) to control the frontend and have pyramids by each TV.

I have set up buttons on the remote to switch between the DVI out and the S-Video out. So if I'm watching the tv in the basement, I activate the S-Video out from the remote, tune the TV to channel 42 and am now watching mythtv in the basement, or any other TV in the house that is set to 42. Now that all the content is in HD, the picture quality suffers from the reduction in resolution of the S-Video output.

I'd like to replace the NTSC modulator with an ATSC modulator. So all the other TVs can get myth in HD. It has been pointed out in the past that a modulator that could take HD component video would have to do mpeg2 compression in realtime to make the ATSC stream and it would be prohibitively expensive.

I was thinking that since myth already has the mpeg stream it captured from the digital tuner, that maybe an ATSC modulator with usb input could just take that stream and modulate it into ATSC RF on the channel of your choice, but I have been unable to find an ATSC modulator anywhere.


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PostPosted: Mon Nov 01, 2010 1:43 pm 
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jzigmyth wrote:
jac1d wrote:
Let me see if I can paraphrase what you're saying:

You would like the ability to play back mythtv content over clearQAM over the coax within your house?

What are you currently using for MPEG-2 capture?

-Jeff
I would like to play back mythtv content over UHF ATSC channels through the coax within my house. EDIT: (8-VSB not QAM)

Let me describe what I am currently doing so you can see where I'm coming from.

I have a combined frontend/backend and only do over-the-air recording of ATSC HD channels from an attic mounted antenna. I have three tuners,a dual HDHomeRun and an HD3000. The video card has DVI out and S-Video out connectors. The DVI is adapted to HDMI and feeds the big screen TV in the livingroom. There are many other small TVs through out the house all connected to a common antenna, through coax.

The S-Video out of the Myth box, along with left and right audio, are connected to a video modulator.( http://www.amazon.com/LABS-1001ST-Stere ... B000FR56IE ) set to UHF channel 42. The output of the modulator is combined into the antenna system and adds channel 42 (mythtv content) to all the other over the air channels in the area.

I use IR remote repeaters ( http://www.smarthome.com/8210/Powermid- ... 01-/p.aspx ) to control the frontend and have pyramids by each TV.

I have set up buttons on the remote to switch between the DVI out and the S-Video out. So if I'm watching the tv in the basement, I activate the S-Video out from the remote, tune the TV to channel 42 and am now watching mythtv in the basement, or any other TV in the house that is set to 42. Now that all the content is in HD, the picture quality suffers from the reduction in resolution of the S-Video output.

I'd like to replace the NTSC modulator with an ATSC modulator. So all the other TVs can get myth in HD. It has been pointed out in the past that a modulator that could take HD component video would have to do mpeg2 compression in realtime to make the ATSC stream and it would be prohibitively expensive.

I was thinking that since myth already has the mpeg stream it captured from the digital tuner, that maybe an ATSC modulator with usb input could just take that stream and modulate it into ATSC RF on the channel of your choice, but I have been unable to find an ATSC modulator anywhere.


You are correct in that there is not currently an affordable, home use, ATSC/QAM single channel modulator available.

There is a solution that will encode and steam over QAM for ~$1000 but I think that puts it outside the realm of options for all but the most committed end users. Arguably moving IP around the house and having a light weight Myth front end is a more cost effective route?

While I understand what you are doing, and I think its a very elegant solution on the SD side of things, I'm not sure how applicable your use case is. I would be interested in hearing from others who are doing or planning something similar.

Unfortunately, the complexity of building the proper MPEG-2 TS from various sources makes live streaming of recorded content more challenging than you might expect. This is especially true when various different capture cards (and thus file structures) are used.

Everything is possible with time, money and imagination. I guess the next question I would like to understand is what do you think is a fair price for a box that does what you would like?

Thanks for your feedback.

-Jeff


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PostPosted: Mon Nov 01, 2010 2:15 pm 
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Location: Lexington, Ky
I'm no expert but I know it is possible to move HDMI around using splitters and signal boosters starting around the $40 range.

That might be a better way to go.


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PostPosted: Mon Nov 01, 2010 3:58 pm 
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Location: middleton wi usa atsc
jac1d wrote:
I guess the next question I would like to understand is what do you think is a fair price for a box that does what you would like?
-Jeff
The NTSC modulator was about $50. I think I would go up to about $200.


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PostPosted: Mon Nov 01, 2010 5:37 pm 
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Given the current bill of materials it is unlikely that you would see an ATSC modulator for $200.

The payload of ATSC transmissions is MPEG-2 Single Program or Multi-Program Transport Stream and it needs to be pre-processed, de-jittered and properl time-stamped before it can be modulated, so it can be properly decoded by the TV. The tech to do all this is just not available yet at these price points.

I think the previous suggestion about HDMI extension is an interesting one that may better suit these kinds of applications.

-Jeff


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PostPosted: Tue Nov 02, 2010 3:45 pm 
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jac1d wrote:
The payload of ATSC transmissions is MPEG-2 Single Program or Multi-Program Transport Stream and it needs to be pre-processed, de-jittered and properl time-stamped before it can be modulated, so it can be properly decoded by the TV. -Jeff
Is the mpeg-2 file that has been captured by Mythtv from an ATSC Tuner already pre-processed, de-jittered and properl time-stamped and ready to be modulated again? Or is it stripped of all that stuff somewhere before it is saved to the hard drive?


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PostPosted: Wed Nov 03, 2010 8:08 am 
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I can't comment on every ATSC tuner, but the one on the cx18 card outputs the entire TS, so it is suitable as a source for retransmission in so far as the full TS is present. If there were multiple programs in that TS, they would also be present in the file itself.

Often on US OTA broadcasts there are two or more channels in the 19.4 Mbps TS. Typically an HD of the main content and an SD sub-channel. For example PBS HD and Create SD.

Someone who has an HDHomeRun could perhaps chime in on whether the HomeRun demuxes the individual programs or not.

The matter of jitter is still present as the file needs to be read from disk and buffered and timed appropriately to go out on the QAM. Timing in the file and timing on the wire are two different things. It isn't as simple as blasting the file out on to the QAM, it has to be paced to stay within specifications to ensure proper playback at the TV.

-Jeff


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