Compressed QAM

[mvallevand]

I decided to rescan my HVR 1600 QAM and I noted that there were 3 new HD 20Mb clear QAM signals (HD CNN, HD A&E and HDNET) on one channel which confused me because the total bandwdith is under 40Mb so I searched and found that the cable company is now compressing the content they are distributing.

http://www.digitalhome.ca/content/view/2425/206/

This came as surprise to me and it certainly something that the Rogers doesn't mention as a new feature.

Martin

[sub]

I'm not 100% sure but I think they're just saying that they're using a variable bitrate, with lower average bitrate (ie, higher bitrate compression) than they would have in the past. I dont think the data itself is being transmitted in any different format.

[mvallevand]

It is more complex then just VBR, I was actually watching it with TSReader (the bit rate fluctuating, not the shows, I know I'm odd). I'm convinced because it's not real compression there will be times that the 3 stations will max out the channel and there will be blockiness. In this example CNN is getting 16Mbs at the expense of the other two

The trouble with cable stb because of all the purchased hardware they can't really change to use H264 or true compression and they are going to sacrifice quality for quantity.

Martin

[sub]

If you expand those PMTs, what does it show the stream types as? This would show you if its still regular MPEG2, or if they're using something like H.264 etc.

[mvallevand]

Regular mpeg 2.

Elementary Stream PID 239 (0x00ef) MPEG-2 Video
MPEG Video: Bitrate 20.000 Mbps Resolution 1920 x 1080i
MPEG Video: Framerate 29.97 fps Aspect Ratio 16:9 Chroma Format 4:2:0
Descriptor: Video Stream Descriptor
Multiple frame rate flag: True
Frame rate: 59.94¼
MPEG-1 only flag: False
Constrained paramter flag: True
Still picture flag: False

Martin

[sub]

Yeah. I just saw the little 'mpg2' icons on the channel images, so its got to be regular MPEG-2, but just re-encoded to a lower bitrate. I think they're varying the bitrate depending on what is happening on other channels, ie if not much is happening on one channel (person sitting talking) then more bitrate is available for other channels that could need it showing action or sports.