Encoding, bandwidth, oh my...

[trparky]

Over at another forum I found an Excel document that contains the mapping of channels based upon what satellite it's carried on along with the transponder. Very cool.

From a quick look at the document it seems that not all channels seem to be broadcasted on DirecTV the same. The HDTV channels seem to be encoded using MPEG-4 h.264. Great. But the SD channels aren't. Why is DirecTV still using the older encoding method for SD channels when MPEG-4 h.264 is so much better?

Also, on average, how many HDTV channels does DirecTV put on a transponder? What is the size of an average HDTV stream in Mbps?

 

[HappyDay]

All the ad boxes on people's homes can't decode a mpeg4 signal so that can't switch to mpeg4 for ad without replacing everyone's boxes. When that happens they will just go to Hi Definition only or as if Hi Definition isn't available. There won't be an Hi Definition and an ad version of the same channel.

That would only cost about a billion dollars if they tried to do it overnight. And I'm not kidding about the cost.

 

[texasbrit]

I think you mean the SD boxes (typo!)
Yes, there are millions of SD receivers out there that don't have MPEG-4 capability.
Channels per transponder varies. See the grid here http://www.dbstalk.com/topic/216782-hd-channel-transponder-grid/
And in most cases the system uses statistical multiplexing to vary the bitrate of each channel based on its demands. So if the channel is showing mainly static pictures, it gets less bandwidth; if it's showing sports, it gets more.

 

[trparky]

What's the total amount of bandwidth a transponder can carry?

 

[texasbrit]

36Mhz.

 

[rad]

Dish has the same issue on their western arc, the SD channels are MPEG2. Plus AFAIK just about all cable companies use MPEG2 for both HD and SD. The common thread to all of them is it costs too much money to replace all those STB's that can't do MPEG4. DIRECT's stopped doing new customer installs of SD hardware and they're hoping that eventually everyone will end up with HD hardware either because they requested the upgrade themselves or have stopped being a customer.

 

[trparky]

36Mhz.

What about in Mbps?

 

[texasbrit]

Sorry, I should have said 36Mbps. Works out around 7Mbps per channel, for a five channel transponder. MPEG-4, which of course requires less bandwidth than MPEG2. Of course the use of stat muxes means that the actual bandwidth for a given channel can be higher or lower than that. And some channels have a contractual agreement to be provided with a minimum bandwidth, I believe HBO used to be 8Mbps. Typically DirecTv has usually allocated channels to transponders so the channels which can get away with lower bandwidth (more static pictures, which the MPEG4 encoders can compress more) are carried on the same transponder as one or two high bandwidth (less efficient compression) channels.

 

[trparky]

I thought I heard somewhere that DirecTV tries to provide at least 7.5 to 8 Mbps per channel to try to maintain as much picture quality as possible. If I understand what you're saying, DirecTV uses more of a variable bitrate as versus a specific finite stream size. The thing is that from second to second the requirements of a picture can change and may require more (or less) bandwidth than it needed a second or two ago. How does DirecTV handle this kind of scenario? How fast can the encoders adapt to the requirements of a particular channel from one second to the next?

Just how good are DirecTV's encoders? I know that not all encoders are created equal and that some are just down right piss poor.

 

[texasbrit]

Yes, DirecTV uses a variable bit rate. Suggest you just google "statistical multiplexers".
DirecTV pretty well follows the development path of transcoders etc I suspect they are using pretty well state of the art equipment. As I understand it, most of the current ones are software based so the algorithms can be refined regularly. I know they used to use ViBE transcoders but don't know if that is still the case.
Don't forget DirecTV is actually transcoding from MPEG-2 to MPEG-4 on most channels.
The technical details are beyond my level of knowledge. Maybe if you post here and at dbstalk with the subject being transcoders you would find someone who can tell you more.

 

[steecoe]

The last few months DTV has been looking like to me they have lowered the bitrate. Picture quality is the one thing that has kept me with DTV for 20 years but it is getting rather disappointing lately...

 

[texasbrit]

from time to time people post that the image quality seems to be not as good as before, but it usually turns out to be temporary (DirecTV is moving around a lot of channels right now) or it's one particular channel (or set of channels). Sports in particular is very variable - ESPN is often pretty rough, but it's that way on cable also. I watched part of a game last week at my friend's house on Time-Warner and it did not look much better than SD.

 

[trparky]

Why would DirecTV be messing with channel placements on their satellites? The phrase "If it ain't broke, don't fix it" comes to mind.

Yeah, the reason why I'm asking is that the picture quality on DirecTV doesn't seem to be as good as it was a few years ago when I had it before. I remember DirecTV being the Gold Standard by which every other pay TV provider was measured up against and failed. Now I don't know, it seems that the picture quality just isn't as good as it once was.

 

[texasbrit]

With the bringing into service of D14/15, there's lots of movement on the HD side particularly the locals.

 

[trparky]

Is DirecTV 14 and 15 due to come online soon?

 

[trparky]

The primary parts of the picture seem excellent but lately I've been noticing that whatever's happening with the encoder it just doesn't know what to do with dark colors. If you pay attention to the dark colors you'll see something that I refer to as "dancing blocks" where you can see compression artifacts dance about on the screen in darker colors.

 

[texasbrit]

D14 TPs have been going active for a while, taking HD locals from the Spaceway sats. The excel chart you found shows which TPs are now carrying locals. We're still waiting for D15

 

[trparky]

Seems that some of my picture quality issues have been because of my TV. My older TV was an LCD TV and one that's 6+ years old. I got a 50-inch 1080p Samsung LED TV for a decent price this week and the difference in picture quality is amazing. Most if not all of my content is 1080p or less so I stayed away from 4K, that and the fact that most of the 4K sets I was looking at were at least $300 more and I just didn't want to spend that at this time when 95% of even DirecTV's content is only 1080p.

 

[ejb1980]

Seems that some of my picture quality issues have been because of my TV. My older TV was an LCD TV and one that's 6+ years old. I got a 50-inch 1080p Samsung LED TV for a decent price this week and the difference in picture quality is amazing. Most if not all of my content is 1080p or less so I stayed away from 4K, that and the fact that most of the 4K sets I was looking at were at least $300 more and I just didn't want to spend that at this time when 95% of even DirecTV's content is only 1080p.

99% of the Directv's content is 720p or 1080i, based on channel. Generally Disney and Fox properties are 720p and Discovery and Universal are 1080i. That is the way the channels are produced and sent to Directv and all providers. Only some of the PPV channels and the HD Channel 125 are 1080p.

 

[trparky]

I meant to say "i" not "p". But yes, most content is still only 1080i.