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wswartzendruber
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PostPosted: Thu Sep 06, 2018 10:46 pm    Post subject: An Idea for ATSC 1.1 Reply with quote

Given the patent licensing debacle surrounding HEVC, it seems like ATSC 3 might be dead in the water before it even takes off. And if that's not enough, any station in the U.S. wishing to broadcast ATSC 3 must broadcast ATSC 1 alongside it. The government is not mandating another switch this time.

It seems like a much more utilitarian approach would be to augment existing ATSC 1 streams with extension data. Theoretically, transmitters wouldn't even need to be modified to support this. Principally, ATSC 1.1 would work by embedding AV1 extension data inside MPEG-2 streams. This would need to be done in such a way that existing ATSC receivers ignored the AV1 data, but 1.1-capable units made use of it. The AV1 data would essentially the delta between the original, uncompressed video stream and what the MPEG-2 encoder managed to maintain. So AV1 would effectively be a delta stream.

Encoding 4K:

1. Downsample copy to 720p.
2. Encode copy as MPEG-2.
3. Decode MPEG-2 copy.
4. Upscale decoded copy back to 4K.
5. Generate 4K delta frame (will be mostly black, except for edges).
6. Encode delta frame with AV1.
7. Embed AV1 data for this frame alongside its MPEG-2 counterpart.

Decoding ATSC 1.0

1. Decode MPEG-2 portion, ignoring AV1 frame.

Decoding ATSC 1.1

1. Decode MPEG-2 portion.
2. Upscale MPEG-2 portion to 4K.
3. Decode AV1 portion.
4. Add both frames together.

We could also look at backporting other features from ATSC 2 and 3 and finding other places inside the parent bitstream for that stuff. We have about 18 Mbps to work with.
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PostPosted: Thu Sep 06, 2018 11:12 pm    Post subject: Reply with quote

Cool story bro.
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richk449
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PostPosted: Fri Sep 07, 2018 1:57 am    Post subject: Reply with quote

If your new approach upscales to 4K from lower resolution signals, why bother?

Why do you care about ota tv? I have a tuner, but it is easier to stream it online. Why doesn’t the government just mandate that all stations have to stream online for free if they want broadcast spectrum?
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PostPosted: Fri Sep 07, 2018 2:24 am    Post subject: Re: An Idea for ATSC 1.1 Reply with quote

wswartzendruber wrote:
Encoding 4K:
Is this not compatible with 8K?

What about DRM? Shortly before I quit paying attention to television technology, I thought I heard some noise about OTA possibly incorporating DRM.
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PostPosted: Fri Sep 07, 2018 3:08 am    Post subject: Reply with quote

richk449 wrote:
If your new approach upscales to 4K from lower resolution signals, why bother?

The AV1 stream contains the 4K resolution that the MPEG-2 stream missed.

richk449 wrote:
Why do you care about ota tv? I have a tuner, but it is easier to stream it online.

Because I utterly despise and hate what the Web has become. Hell, I have a little AM radio now that I've kicked iHeartRADIO to the curb for changing my default station to be some Gay Pride thing.

richk449 wrote:
Why doesn’t the government just mandate that all stations have to stream online for free if they want broadcast spectrum?

It increases costs for the stations who already have a suitable means of reaching the local population.
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wswartzendruber
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PostPosted: Fri Sep 07, 2018 3:09 am    Post subject: Re: An Idea for ATSC 1.1 Reply with quote

pjp wrote:
wswartzendruber wrote:
Encoding 4K:
Is this not compatible with 8K?

AV1 can handle 8K, I think

pjp wrote:
What about DRM? Shortly before I quit paying attention to television technology, I thought I heard some noise about OTA possibly incorporating DRM.

DRM is something that never really took off with ATSC. It's in the spec, but I've never come across a locked channel anywhere I've lived.
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PostPosted: Fri Sep 07, 2018 4:16 am    Post subject: Reply with quote

wswartzendruber wrote:
richk449 wrote:
If your new approach upscales to 4K from lower resolution signals, why bother?

The AV1 stream contains the 4K resolution that the MPEG-2 stream missed.

I see. So you mean that of every four pixels, one would come from the MPEG-2 portion, and three would come from the AV1 portion?

Quote:
richk449 wrote:
Why do you care about ota tv? I have a tuner, but it is easier to stream it online.

Because I utterly despise and hate what the Web has become. Hell, I have a little AM radio now that I've kicked iHeartRADIO to the curb for changing my default station to be some Gay Pride thing.

Okay. Once you hit the fullscreen button, you can't tell if it was coming from the web or over the air.
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Akkara
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PostPosted: Fri Sep 07, 2018 5:22 am    Post subject: Reply with quote

richk449 wrote:
Why do you care about ota tv? I have a tuner, but it is easier to stream it online.

Because not everyone has the bandwidth to stream 4K (nor, for that matter, even 2K).

Because, even if there is enough bandwidth, &^*# "ISP"s love to re-encode to lower quality to save themselves on costs. Or to throttle it to make their own video service seem better than it is.

Because, depending on how many viewers are watching a show, broadcasting is thousands of times more efficient than sending out that many individual streams.

Because streaming is often laden with restrictions.

Because no third-party site needs to know what I'm watching.

Because broadcast works even when the net is down.

Reasons enough?


Getting back to OP's proposal. It is an interesting idea. Would be great if it can be made to work well. But I foresee some difficulties in regards to encoding the difference-signal. I expect there will be as much energy due to mpeg2 compression artifacts, as there is in image-delta energy. Ever try to encode some audio as a mp3, then subtract the result from the original source? It is far from "a small residue" that's left. I expect a similar thing would be true with compressed video. (Although I have to admit to not having worked with video, so I can't say for sure.)

Before compression, 4K has 9x as much data as 720p. It isn't clear that using the 720p as a springboard will achieve much additional savings. I would not be surprised if it ends up that sending two separate streams is about the same bandwidth as trying to use one for the other. The motion-vectors would be too coarse by a factor of three in each dimension. I also hear rumors they might be moving away from the easy-to-implement but non-ideal sum-of-absolute-differences metric, to one that's based on convolution and finding points of minimum residual energy. And there's machine-learning-based stuff I hear mention of. Those techniques, if they can be made to work, can bump compression ratios to even higher levels with minimal quality loss.

The low/hi res stream idea might be workable if the 720p-encoder is tweaked taking into account the dual-resolution, so that it produces output that is more useful to the 4K encoder. The result might be that the 720p-only portion might not look quite as nice on a standard 720p receiver. It would be like the signal degradation tradeoff that was accepted on old black & white TVs, in order to overlay color information onto the same band.
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PostPosted: Fri Sep 07, 2018 5:34 am    Post subject: Reply with quote

Akkara wrote:
richk449 wrote:
Why do you care about ota tv? I have a tuner, but it is easier to stream it online.

Because, depending on how many viewers are watching a show, broadcasting is thousands of times more efficient than sending out that many individual streams.

This is the interesting one.

Is it true?

If so, can you explain why?

It is not as if OTA TV transmission is a "energy efficient" - a common transmitter is 50 kW.
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PostPosted: Fri Sep 07, 2018 5:51 am    Post subject: Reply with quote

Don't forget you can broadcast online too.
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PostPosted: Fri Sep 07, 2018 6:33 am    Post subject: Reply with quote

richk449 wrote:
It is not as if OTA TV transmission is a "energy efficient" - a common transmitter is 50 kW.

Yeah, but if you do the numbers - the break even point over sending traffic through users' home networks (wifi isn't exactly power efficient either...) is probably only in the tens of thousands of watchers.
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PostPosted: Fri Sep 07, 2018 7:00 am    Post subject: Reply with quote

richk449 wrote:
It is not as if OTA TV transmission is a "energy efficient" - a common transmitter is 50 kW.

And a datacenter takes how much power? I don't have hard numbers handy, but last I heard the racks are in the range of tens of kilowatts each.

(Although originally I had been thinking "efficient" in terms of not having to send thousands of copies of the same bits over and over again, and the resulting network-clogging traffic. But now that I think about all the servers, routers, and everything else that goes into supporting streaming video, OTA broadcast is probably more efficient in the energy sense as well.)
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PostPosted: Fri Sep 07, 2018 5:16 pm    Post subject: Reply with quote

I think it would be best to scale each block of MPEG-2 individually so as to have no bleed between blocks when the AV1 encoder hits it.

All MPEG-2 blocks are 16x16. Coming from 720p, these would each get scaled to 48x48 blocks for the AV1 encoder to handle. While this wouldn't take advantage of the encoder's full 64x64 superblock capabilities, it could still work at the 48x48 level and then subdivide each block recursively as it desires, down to the 4x4 level.

EDIT: Actually, AV1 might not be able to start with 48x48 blocks.

EDIT: BLAH! Scratch all that! I'm pretty sure AV1 won't recursively encode a 48x48 block because it's not an even power of two. The best thing to do would be to put the decoded MPEG-2 frame through a deblocking filter before sending it to AV1.
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PostPosted: Sat Sep 08, 2018 2:20 pm    Post subject: Reply with quote

wswartzendruber wrote:
I think it would be best to scale each block of MPEG-2 individually so as to have no bleed between blocks when the AV1 encoder hits it.

All MPEG-2 blocks are 16x16. Coming from 720p, these would each get scaled to 48x48 blocks for the AV1 encoder to handle. While this wouldn't take advantage of the encoder's full 64x64 superblock capabilities, it could still work at the 48x48 level and then subdivide each block recursively as it desires, down to the 4x4 level.

EDIT: Actually, AV1 might not be able to start with 48x48 blocks.

EDIT: BLAH! Scratch all that! I'm pretty sure AV1 won't recursively encode a 48x48 block because it's not an even power of two. The best thing to do would be to put the decoded MPEG-2 frame through a deblocking filter before sending it to AV1.

This may all be true, but your new avatar triggers me.
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