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Discussion Starter · #1 ·
Hello,

could somebody tell me , what's the video resolution , average bitrate on 721 or any other dish pvr ?

or maybe somebody could give me a little video sample ... I would greatly appreciate it.

thx a lot :)
 

· Godfather
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The 721 records the MPEG stream that is transmitted. So it have the same resolution of any other Dishnetwork box (other than HD content, which the 721 cannot record). The actual data rate and PQ (picture quality) depends on the channel you are looking at. I'd recommend looking at a display at one of the retail outlets that carries Dish. Sears, SAMs club, and (shudders) Walmart. Sears is the most likely to have an actual dish feed hooked up you can mess with.
 
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Discussion Starter · #3 ·
ok ... I myself have dish ...

so, the quality is about the same as you see it on tv ? ... b/c like if you look at most VCDs for example, which has mpeg too , the quality is worse than the dish ...

maybe someone can point me to the info about dish mpeg signal ?

thx
 

· New Member
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Standard VCDs use MPEG-1 video. This is why they look the way they do. It is often compared to VHS quality, however all MPEG video quality can vary greatly.
Dish streams are MPEG-2. You may have seen other MPEG-2 format video on SVCDs or DVDs. And as have noticed the quality is much better.
For more information about (S)VCDs and DVDs you can visit: http://www.vcdhelp.com/
 

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I capture video into my computer using a Matrox video capture card. The software utilities report the properties of the video stream.

When attached to my 501, the capture card detects a 704 (columns) x 480 (rows) array of pixels. The vertical refresh rate is 29.97 Hz (frames per second).

The bit rate is normally the product of the width * rows * refresh_rate * color_depth.

I would assume that the color depth is 3*24 (24 bits of color * 3 colors). It may actually be fewer bits of color (depends on the video compression codec used). Usually it is between 16 and 24 bits.

If you accept the assumption, the bitrate would be:
704*480*29.97*3*24 = 729177292.8 bits/sec (697 Mega bits per second/87 Mega bytes per second).

Of course, this is a raw uncompressed video stream. In the digital world, you never leave your video stream uncompressed. Without a raid array, most hard drives cannot keep up let alone store a significant length of video.

Dish and DSS both move the data around as MPEG-2 compressed streams. The DVD format is built around MPEG-2 compressed video. Divx (popular with the computer crowd) is an implementation of the MPEG-4 compression standard.

Back to the resolution of my 501, even though my capture card reports 704x640, there is usually 15-12 columns (mostly on left side of captured video) and 9 rows (mostly on the bottem of captured video) of noise on my captured video stream. This may be an artifact of my capture card or an artifact of the 501. My old reciever, a 5000 model, had the same amount of noise.

BTW, my brothers DSS system captures in as 640x480 with no noise when captured with a Hauppauge capture card.



cheers
 
G

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Discussion Starter · #6 ·
Originally posted by rj_in_ut
...If you accept the assumption, the bitrate would be:
704*480*29.97*3*24 = 729177292.8 bits/sec (697 Mega bits per second/87 Mega bytes per second)...
Hmmm. Doubtful. Professional media platforms (video servers) such as the Grass Valley Group Profile XP1000 series typically use rates between 8 and 40 Mb/s. Most TV stations and networks use 12 or 15 Mb/s for encoding NTSC video into their servers, usually with long GOPs and at 4:2:2. While I'm not sure about this next little factoid, I've seen 1.5 Mb/s quoted as the norm for DBS delivery.
 

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More like 1.8- 2.0 MB/s for standard channels, maybe up to 2.5 (maybe more) for a fast action Premium channel. Sky Angel is probably approaching 1.0 - 1.3 (all their compression).

Funny you should mention the "noise" on a computer capture card -
I have a Hauppage WinPVR250, and in "DVD Quality" video mode, I see noise at the top of my "TV screen". I haven't noticed any noise on the bottom yet.

But none of this "noise" is displayed on my TV.
 

· Banned
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This noise is the Close Captioned signal and possibly other data which is hidden in the lines which should be out of view of most TV sets.

I looks like little white things jumping around in the black line.

Nothing to worry about though everything is running ok on your system.
 

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Don't confuse compressed vs. uncompressed bit-rate. Also don't confuse bits per sec (bps) vs. kilo bits per second (kbps - bps/1024) and Mega-bits per second (kbps/1024).

I would guess that the numbers that most people usually hear quoted are the rates that are transmitted over some kind of a communication link. Digital video is NEVER streamed uncompressed. Even my old 600MHz Duron system could do a lossless software HUFFYUV codec that yeilds 2.3 - 2.8 compression ratio in real time. This is very common for real time video capture. The last episode of A&E's Nero Wolfe I compressed (time-shifting for private viewing later folks *GRIN*) using Divx 5.02 with a resolution of 512x352 yeilded a final audio+video bit rate of 112 kbps (0.109Mbps). If I had compressed the same program to a MPEG-2 I would probably set the bitrate to 800kbps.

Originally posted by TomCat


Professional media platforms (video servers) such as the Grass Valley Group Profile XP1000 series typically use rates between 8 and 40 Mb/s. Most TV stations and networks use 12 or 15 Mb/s for encoding NTSC video into their servers, usually with long GOPs and at 4:2:2. While I'm not sure about this next little factoid, I've seen 1.5 Mb/s quoted as the norm for DBS delivery.
Those rates sound right to me. 8 - 40 M-bytes/s should be about right for a lossless codec. 8 - 40 M-bits/s should be about right for a good low-loss codec. 1.5 Mbps makes sense for a MPEG-2 stream running wide open (optimised for video quality not bitrate) like the way DVDs/Satalite systems usually run.
 
G

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Discussion Starter · #10 ·
No confusion here. You may have noticed I used the terminology "Mb/s", which stands for Megabits per second. "MB/s" would be the terminology for Megabytes per second.

Uncompressed? MPEG-2 encoding is compressed by definition...a combination of a number of compression algorithms to reduce the amount of bits needed to convey necessary information. It is never lossless (information is indeed discarded so the original information can't be reconstituted 100% faithfully), but it is very robust and if done properly the losses are not at all noticeable.

A few years ago I did some tests to see how low of a bit rate I could go to before degradation was noticeable in order to decide what bit rate we would use in our facility. At the time, storage media was much more expensive and we were finding it difficult to store more than about 2000 minutes of video for a commercial playback system. Using a 17 frame GOP and 4:2:0 and encoding extremely "busy" video (white-water rafting footage and a clip of a vat of quarters being poured onto a table) I found that I could approach down to 6 Mb/s before the encoders became bit-starved and started to pixellate. Of course we were also encoding 4 audio channels and 1 timecode channel in the same bitstream, which takes up about 8-9% of the bits. We chose 10 Mb/s just to be safe. Today, now that we have 60 181GB drives capable of storing well over 1500 hours of video, we use 12 Mb/s.

There are two other major factors in DBS distribution, VBR (variable bit rate) and statistical multiplexing, both used to smooth out the peaks of bit demand in a multi-channel delivery system, so calculating the actual bit rate of a single DBS channel is both a moving target and a complex issue dependent upon all of the other channels being transmitted. VBR is usually limited to some small percentage, however, so that low-cost decoders in the STB's can keep up.
 

· Legend
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Echostar uses VBR and statistical multiplexing (Harmonic FYI) so it's difficult to say exactly what the bit rate is.

However, on a typical high-power 24MHz transponder you get about 40 Mb/s with QPSK and appropriate error-correction. Echostar usually puts about 10 channels on each transponder plus some data feeds (s/w updates, EPG data, OpenTV apps, etc.) That works out to about 3.5 Mbps per channel AVERAGE. VBR allows channels to use bandwidth as they need it (i.e. use more when there's lots of action, and less when there's not).

It is the raw feed from the satellite that is recorded on satellite PVR boxes (as opposed to stand-alone PVRs which have analog signal digitizing hardware in them.... that's why you have a choice on video "quality" for stand-alone PVRs, but none for satellite based PVRs)

-Rich

BTW: This is typically much better quality then you get through digital cable. Many digital cable feeds come from the AT&T HITS program (head-end in the sky). This program delivers a full package of programming to the cable company and saves them tons of money in multiplexing equipment. Unfortunately, AT&T makes the most of their limited bandwidth and typically encodes signals down to 2MBps or even less. Just another way that Satellite is better than digital cable!!
 
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