Detroit ATSC 3.0 - Jan 2021

[PCTools]

You should maintain the ASTC 3 channels as well.

[thully]

The latest system software update for my Chromecast seems to have fixed the 107.1 stuttering issue. So that was indeed an issue with the Chromecast firmware.

[nickk]

We have 102.1 and 107.1 playing smoothly on Android and AppleTV. Win10 was already working.

Android app update was submitted today.

Nick

[jimbolaya]

You should maintain the ASTC 3 channels as well.

Yeah, it was weird. When I checked the next day all the HEVC stuff was there.

Of course, now I just have to see some 4K broadcasts. They're all still 1920x1080, but HEVC so I can't hear the audio in Linux (yet).

[PCTools]

Would be curious on what bit rate you are witnessing thru the HDHomerun gui.

Depending on the scene, I would hope they are averaging from from 1 Mbit/s to 57 Mbit/s.

Hopefully, more towards the upper end in the 50's.

Please report your bit rates, so I can see if the HDHomerun is in fact throttling the signal.

Thanks

[signcarver]

Would be curious on what bit rate you are witnessing thru the HDHomerun gui.

Depending on the scene, I would hope they are averaging from from 1 Mbit/s to 57 Mbit/s.

Hopefully, more towards the upper end in the 50's.

Please report your bit rates, so I can see if the HDHomerun is in fact throttling the signal.

Thanks

I think you are crazy expecting any tv stream to be so high. First it is HEVC so generally 1080p would have a max of 6-8Mbps with most around 4-5. The bandwidth is shared so nothing should ever be expected to be more than half of that rate (57) and generally shouldn't be expected to be a quarter of that rate, second to be able to be seen by more people (not in just the first 2-5 miles) that max will generally be a lot lower than 57 (I wouldn't expect more than 38).

[nickk]

If the modulation is configured for 50Mbps then figure broadcasters are more likely to put 20-odd sub channels on it rather than give 50Mbps to one stream.

[jasonl]

Our old friends Nyquist, Shannon, and Hartley guarantee that you'll never see 50+Mb/s on an ATSC 3 broadcast in the real world, at least not on the 6MHz channels used in North America. The modulation settings that can generate a data rate that high require a signal so perfect that you basically need an outdoor antenna with perfect line of sight to even have a chance. That's a non-starter for any station since it would prevent most people from ever receiving their station. Most stations are running settings that more or less match their original ATSC broadcast, so they don't get much (if any) increase in available bits.

[PCTools]

As a baseline, the bit rate of the signal can be view in the Hdhomerun gui.

What results are you witnessing?

[PCTools]

A 6 Mhz channel would cap at a bit rate of 57 Mbps.

ATSC 3.0 capacity is estimated to be 26 Mbps, while ATSC 1.0 is around 19.4 Mbps.

So, moving to 4K will yield ~ 33% increase in bit rate.

On a side bar note, to take full advantage of 8K you would need 200 Mbps and ATSC 3.0 standards do not support this.

Our old friends Nyquist, Shannon, and Hartley guarantee that you'll never see 50+Mb/s on an ATSC 3 broadcast in the real world, at least not on the 6MHz channels used in North America. The modulation settings that can generate a data rate that high require a signal so perfect that you basically need an outdoor antenna with perfect line of sight to even have a chance. That's a non-starter for any station since it would prevent most people from ever receiving their station. Most stations are running settings that more or less match their original ATSC broadcast, so they don't get much (if any) increase in available bits.

[jasonl]

Yes, 57Mbps is the theoretical max, but you would need a minimum of ~33dB SNR to receive that, which I believe would correspond to 110% signal quality on the HDHomeRun's ATSC 1 scale. I live within 20 miles of the broadcast towers and I can't even reliably get 100% on anything.

[thully]

What kind of quality are people seeing on the ATSC 3.0 channels? In my experience, the video on ATSC 3.0 seems a tad inferior to ATSC 1.0. In particular, one thing I’m noticing is that white text (such as the ticker on sports) tends to have a rainbow tinge. I’ve seen this on multiple channels (7/62 for sure, and I think I’ve seen it on 2/4). I’m hoping they can at least get the quality up to match ATSC 1.0 and perhaps better (1080p on all channels would be nice, even if 4K is a ways off). The bitrate is obviously lower (which is an advantage as far as how much space DVR recordings take), though HEVC is designed to get higher quality with smaller bitrates.

[cincylion]

Comparison of the difference in file sizes on two recordings of the same half hour show, one ATSC 3.0 vs ATSC 1.0. The ATSC 3.0 file is about 60% smaller.
WJBK-Detroit

ATSC 3.0
Complete name :FOX2 Sports Works 2021-02-14-2300.mpg
Format : MPEG-TS
File size : 768 MiB
Duration : 29 min 59 s
Overall bit rate mode : Variable
Overall bit rate : 3580 kb/s
Width : 1920 pixels
Height : 1080 pixels
Display aspect ratio : 16:9
Frame rate : 59.940 (60000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 10 bits
Color range : Limited


ATSC 1.0
Complete name :FOX2 Sports Works 2021-02-14-2300.mpg
Format : MPEG-TS
File size : 1.88 GiB
Duration : 29 min 59 s
Overall bit rate mode : Variable
Overall bit rate : 8965 kb/s
Width : 1280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Active Format Description : Full frame 16:9 image
Frame rate : 59.940 (60000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits

[CBme]

Comparison of the difference in file sizes on two recordings of the same half hour show, one ATSC 3.0 vs ATSC 1.0. The ATSC 3.0 file is about 60% smaller.

ATSC 3.0
Complete name :FOX2 Sports Works 2021-02-14-2300.mpg
Format : MPEG-TS
File size : 768 MiB
Duration : 29 min 59 s
Overall bit rate mode : Variable
Overall bit rate : 3580 kb/s
Width : 1920 pixels
Height : 1080 pixels

That is strange and interesting that your FOX station is being uprezzed to 1080 at the lighthouse instead of leaving it at 720p. I can't even speculate as to why they would do that.

[csdesigns]

In my experience, the video on ATSC 3.0 seems a tad inferior to ATSC 1.0. In particular, one thing I’m noticing is that white text (such as the ticker on sports) tends to have a rainbow tinge. I’ve seen this on multiple channels (7/62 for sure, and I think I’ve seen it on 2/4).

This can be resolved by better encoder settings at the station. Sounds like a chroma issue, which is something that can happen if the encoder is deinterlacing incorrectly, or the scaler being used is poor. If the station is upscaling the source 1080i to 1080p output, then this is the likely culprit (it would also be possible on 720p to 1080p upscaling). The other culprit could be the decoder, particularly if they are outputting '1080i' HEVC.

That is strange and interesting that your FOX station is being uprezzed to 1080 at the lighthouse instead of leaving it at 720p. I can't even speculate as to why they would do that.

While certainly an outlier, this doesn't sound too odd. FOX has been wanting to move to 1080p for a while now, especially at the stations that are owned by the Network, so this could just be their attempt to prepare for that eventuality. I doubt the source content the station is receiving is in 1080p format, but hopefully by the time the 2021 NFL season starts (or possibly even the 2021 MLB All-Star game or maybe a big NASCAR event – COViD permitting of course), 1080p will be more ubiquitous from FOX.