ATSC MPEG2 vs. MPEG4 Compression? - Canadian TV, Computing and Home Theatre Forums
 

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Old 2009-04-23, 02:43 PM   #1
RingtailedFox
 
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Question ATSC MPEG2 vs. MPEG4 Compression?

I know that most digital televisions recieve programming encoded in MPEG 2 compressed format... I also know that ATSC has approved of MPEG 4 as a valid compression format... does this mean my new TV will be worthless/unable to decode any MPEG 4-encoded programs? do i need a new TV or set top box, or will a simple "software upgrade" via USB do the trick (my TV has a USB port for this, and apparently, it can handle software updates)?
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Old 2009-04-23, 02:50 PM   #2
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The ATSC digital OTA broadcast standard specified MPEG2 compression until very recently when the superior MPEG4 was also added. No ATSC broadcasters anywhere (except in test labs) currently use MPEG4, and no plans have been announced to roll it out anywhere yet.

As for today's receivers, the tuner section of the circuitry would not require any changes. The processing section would definitely have to be made MPEG4-compatible, but there is no data I've found that indicates if this can be done via software upgrade or whether new chipsets will be required.

The chief benefit of broadcasting with MPEG4 compression in the future is that a single transmitter covering 6MHz of bandwidth could conceivably carry several simultaneous HD channels as opposed to the present bandwidth limitations of MPEG2 that allow only one HD channel or several SD channels.
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Old 2009-04-23, 05:51 PM   #3
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MPEG4 is much more computationally intensive to decode than MPEG2 and hardware specifically designed to decode MPEG2 cannot do MPEG4 - they're just too different. A PC is different, because the CPU is a multi-purpose processor, though it will still churn harder to decode MPEG4 than MPEG2. For saving video streams onto disk (ie. PVR/HTPC), I imagine there would be no decoding, just outright saving of the datastream like there is on MPEG2, so that wouldn't require any additional hardware. It would just be the playback (hehe, 'just') that would be affected.
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Old 2009-04-23, 07:25 PM   #4
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I don't see the change happening. With the current policy attitude towards OTA broadcasting, there isn't an immediate need to increase capacity. Unless of course governments in Canada and the US decide to auction off more of the spectrum currently used for OTA--then we'd need to improve capacity.
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Old 2009-04-23, 08:32 PM   #5
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The main difference though, is that IF there is a transition, it's not a major platform change.
You can still have one MPEG2 stream and MPEG4 stream(s) going to support both old and new chipsets.
E.g. maybe in a few years they will allow a simulcast - one stream in MPEG2 the other in MPEG4.
Eventually, after a transitional period, they can drop the MPEG2 stream and replace it with a couple more MPEG4's (or bump up the quality of the MPEG4)

Just a thought.
Analogue -> digital was the huge step.
Everything else is just a software change (or can at least be mitigated more easily)
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Old 2009-04-23, 08:56 PM   #6
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Honestly, I really don't see the US or Canada transitioning to MPEG-4 period. Look how much trouble they had going from analog-to-digital. This would effectivly be the same thing.
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Old 2009-04-23, 11:40 PM   #7
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I also question MPEG4's performance in weaker signal conditions and/or during weather. You'll likely end up with longer drop-outs....
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Old 2009-04-24, 11:25 AM   #8
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The ability to reassemble the digital signal would be a function of the FEC circuitry and buffers, not the MPEG4 processing itself. So as long as the signal is adequate for a lock, the quality will be proper. There was much discussion in the ATSC about MPEG4's suitability prior to its acceptance.
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Old 2009-04-24, 11:50 AM   #9
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The likely situation is that most standalone ATSC receivers (TVs and STBs) will be obsoleted becasue their hardware is only MPEG2 capable. TVs would need replaced or have an external STB added, or STBs replaces, if their hardware cannot support MPEG4 with a software update. Modular TVs could just have a module board replaced.
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Old 2009-04-24, 12:44 PM   #10
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As I understand the ATSC spec, the primary channel (.1?) must be MPG2, so even if stations started sending MPG4 on subchannels, the boxes wouldn't be totally obsolete. This seems genius to me - it builds in major incentives to move people to more capable devices without forcing anyone to change.

And as I understand the spec, most (all?) of the error correction is built into the transport layer, so if you can lock onto a signal carrying MPG2 data, you'd be able to lock equally well onto that signal carrying MPG4 data - just like today if you can lock onto any one subchannel, you've locked onto all of them.
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Old 2009-04-24, 12:48 PM   #11
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Correct, the Forward Error Correction is in the Transport Stream and its local buffers - that's the point I was making in Post #8.

Also even if the primary channel is in MPEG2 format it can be left running just a barebones data stream in order to free up the bandwidth for the others.
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Old 2009-04-25, 01:29 AM   #12
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so, my one-year-old Samsung television won't be obsolete? i was hoping on keeping the LCD set for at least ten years, and i will do anything i can to not throw it out. If i recall, a couple stations already offer two streams of 720p data...an example is here: http://en.wikipedia.org/wiki/Digital...nnel#Tradeoffs
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Old 2009-04-25, 01:51 AM   #13
Jase88
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Quote:
Originally Posted by RingtailedFox View Post
i was hoping on keeping the LCD set for at least ten years, and i will do anything i can to not throw it out.
I wouldn't count on that. I don't see most flat panels (especially Plasma) lasting a decade. You might do better if your panel has LED backlighting....
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Old 2009-04-25, 10:42 AM   #14
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Your display won't be obsolete, but if technology advances you may feel a strong incentive to replace it, or at least enhance it with an outboard STB.

Of course, that's a *big* if. If anyone has plans to start broadcasting MPG4, I haven't heard it. There are pretty big incentives not to (no audience for it initially).

And at over $1,000 I too expect my TV investment to last a long time, though not quite 10 years. If I can get 5 years out of it that's acceptable. At 9 years (about $10/month average) I call it a good investment.
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Old 2009-05-02, 09:15 PM   #15
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Stage one will be to design new chipsets that support MPEG4. Eventually all new TVs will have one of these chipsets. Once enough people own TVs that support MPEG4, some broadcasters may start to use it. It certainly will be much less disruptive than the conversion from analog to digital as all they need to change is their MPEG encoder. As said earlier, they will likely initially only have subchannels use MPEG4 so people who's TVs don't support it, will still be able to receive the main channel. Eventually they may only broadcast in SD (to save bandwidth) in MPEG2, but this will be a long ways down the road.
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