| Compression The best HD quality is transmission w/out compression. Except for over-the-air, the providers all compress from what I understand. But frankly, I'd rather have more HD channels than true uncompressed HD. |
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| said by compression :
The best HD quality is transmission w/out compression. Except for over-the-air, the providers all compress from what I understand. But frankly, I'd rather have more HD channels than true uncompressed HD.
OTA is compressed as well.
What one can do to determine who has the best quality is to analyze the transport stream of all the vendors.
OTA has a max bitrate of about 19.4Mbps
DirecTV is usually around 8-12Mbps
Neal |
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 AlpinePremium
join:2000-01-11
Atlanta, GA | Aren't the MPEG4 channels on DTV (ie, the locals) better than the MPEG2 (nationals?)
I thought I've heard that before and my experience (I've got DTV-HD) bears that out.
90% of the time all looks great. When I have picture quality problems it generally stems from the original feed. Some broadcasts are just better than others..
Adam |
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 ColorBASIC8-bit FunPremium
join:2006-12-29
Corona, CA | I don't know about D* but I can definately tell the difference between E* HD locals vs OTA locals. |
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| reply to compression
Based on the size of MythTV recordings I've made both on Comcast and OTA, I believe Comcast compresses about the same as the broadcast networks. It's not exactly the same data, though; the OTA seems to have slightly higher contrast. I would guess that Comcast gets a high-bandwidth feed from the stations, and then compresses itself using slightly different equipment than the station uses for its broadcast. |
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 djrobx
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1 edit | reply to Alpine
quote:
Aren't the MPEG4 channels on DTV (ie, the locals) better than the MPEG2 (nationals?)
DirectTV's Mpeg-4 video probably comes from the MPEG-2 source. In other words, they transcode to mpeg-4. Transcoding always results in video that's inferior to the original.
Cable companies typically just pick up and rebroadcast the compressed OTA signal, although they could recompress it if they so desired. Over on the AVS forum, Comcast was quoted as having a "no recompression" policy although I don't know the validity of that.
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Laser eye surgery rocks! I love frickin' laser beams. |
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| reply to compression
4DTV on a Cband/Kuband is uncompressed but you have to have a 7 to 10 foot dish. The BUD picture on both analog and digital are far superior to the picture of Cable and DBS.
After all were do you think Cable and DBS get their feeds from? 4DTV is the consumer version of what the networks feed out to cable and dbs providers. |
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| reply to Alpine
said by Alpine:Aren't the MPEG4 channels on DTV (ie, the locals) better than the MPEG2 (nationals?) I thought I've heard that before and my experience (I've got DTV-HD) bears that out. 90% of the time all looks great. When I have picture quality problems it generally stems from the original feed. Some broadcasts are just better than others.. Adam I believe that the MPEG4 locals run about the same picture quality (slightly lower bit rate) as the MPEG2(East and West coast feeds)locals on DTV. I believe they run a lower bit rate and put more channels in the same space, however I have not seen a transport stream from a MPEG4 transponder.
I would argue that any quality issues that you see though DirecTV system are the responsibility of DirecTV and not the network feeds. Most all network distribution runs 30 - 40Mbps and some much higher. The bandwidth limitations kick in at DirecTV.
Neal |
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| reply to battleop
said by battleop:4DTV on a Cband/Kuband is uncompressed but you have to have a 7 to 10 foot dish. The BUD picture on both analog and digital are far superior to the picture of Cable and DBS. After all were do you think Cable and DBS get their feeds from? 4DTV is the consumer version of what the networks feed out to cable and dbs providers. ANYTHING you see via satellite is compressed. There are no delivery systems in place to serve uncompressed HD-SDI/Analog HD video to consumers.
Neal |
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djrobx
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1 edit | reply to battleop
Truly uncompressed HDTV would require a *massive* stream. I have a hard time believing anyone broadcasts an "uncompresed" HD stream. When people refer to OTA's superior "uncompressed" stream, I think they really mean "un-recompressed".
Consider 1080i:
1920 (Horizontal pixels)
x
540 (540 lines per field)
x
60 (60 fields/frames per second)
x
16 (16 YUV bits)
---------------------------------
995,328,000 bits per second
So, excluding audio, they would need about 1 gbps just for a single channel, vs 19.2mbps for the de-facto "19.2mbps" standard.
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Laser eye surgery rocks! I love frickin' laser beams. |
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| said by djrobx:Truly uncompressed HDTV would require a *massive* stream. I have a hard time believing anyone broadcasts an "uncompresed" HD stream. When people refer to OTA's superior "uncompressed" stream, I think they really mean "un-recompressed". Consider 1080i: 1920 (Horizontal pixels) x 540 (540 lines per field) x 60 (60 fields/frames per second) x 16 (16 YUV bits) --------------------------------- 995,328,000 bits per second So, excluding audio, they would need about 1 gbps just for a single channel, vs 19.2mbps for the de-facto "19.2mbps" standard. Although your math is not correct for how HD-SDI is constructed your idea is correct.
Neal |
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djrobx
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| That's simply a calculation of the number of uncompressed bits in the video frames, not math for a specific protocol, although I'd be happy to see the math for HD-SDI. 
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AlpinePremium
join:2000-01-11
Atlanta, GA | reply to A900MHz Fan
Two things:
1. I don't believe D* transcodes from MPEG2 to MPEG4. I believe it's recompression from the original OTA (or direct digital feed in some cities) source. The fact that the MPEG4 channels look BETTER than the MPEG2 seems to back this up.
2. Quality issues certainly can be D*'s problem, but I've often seen shows on the same network be inferior to others on the same network. CBS's golf broadcasts, for example, are hit or miss. The "shows" on CBS, however, are generally excellent quality. Same network, different quality = network issue rather than D*.
Adam |
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| reply to djrobx
said by djrobx:That's simply a calculation of the number of uncompressed bits in the video frames, not math for a specific protocol, although I'd be happy to see the math for HD-SDI. Right, you are assigning only one bit per pixel with your math, thus you could only ever transmit one color.
From a camera standpoint (generally)
Y analog to digital channel is sampled at 74.25MHz
Pb analog to digital channel is sampled at 32.125MHz
Pr analog to digital channel is sampled at 32.125MHz
The three video channels are multiplexed into a parallel 10 bit stream.
74.25MHz x 10(bit mux) = 742.5Mbps
37.125MHz x 10(bit mux)= 371.25Mbps
37.125MHz x 10 (bit mux)= 371.25Mbps
TOT = 1.485Gbps
Neal |
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djrobx
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| quote:
Right, you are assigning only one bit per pixel with your math, thus you could only ever transmit one color.
That's what the 16 YUV bits in my math is for, which is roughly equivalent to 24 bit RGB color. If 30 bit YUV is standard then we can go with that.
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djrobx
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1 edit | reply to Alpine
quote:
1. I don't believe D* transcodes from MPEG2 to MPEG4. I believe it's recompression from the original OTA (or direct digital feed in some cities) source.
The OTA feed is MPEG-2. I find it highly unlikely that D* and some stations are setting up fiber multi-gigabit links just to transmit the uncompressed stream for a relatively small increase in quality.
-- Rob
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Laser eye surgery rocks! I love frickin' laser beams. |
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| reply to Alpine
D* has to transcode to MPEG4, no locals broadcast in MPEG4, so the source feeds to D* are MPEG2 signals. D* may run the same number of MPEG2 and MPEG4 channels per transponder, thus giving the MPEG4 channels more bps and better quality, I am not sure on that issue.
One thing to watch for especially in golf is that not all the cameras at the remote event are HD. Many shots are up-converted 16:9 SD cameras. It is very expensive for networks to work with and rent 50 to 60 high end HD cameras ( @ 100k-150k each).
Neal |
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AlpinePremium
join:2000-01-11
Atlanta, GA | quote:
One thing to watch for especially in golf is that not all the cameras at the remote event are HD. Many shots are up-converted 16:9 SD cameras. It is very expensive for networks to work with and rent 50 to 60 high end HD cameras ( @ 100k-150k each).
That makes sense. A lot of the shots seem very much like 16:9 SD. I'd prefer they use normal 4:3 SD cameras and put bars on the side (like ESPNHD) rather than try to pass off 16:9 SD as true HD.
I long for the days that all new broadcasts are HD!
Adam |
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