dslreports logo
    All Forums Hot Topics Gallery


how-to block ads

Search Topic:
share rss forum feed


Boulder, CO
reply to cypherstream

Re: [HD] Get Ready for "Ultra-HDTV"

said by cypherstream:

Ok, the thing with MPEG4 is that sometimes the color gamut is compressed more so than seeing "mosquito noise" like in MPEG2. The resolution is sharp and crisp for much less bits per second, but color representation can suffer. Faces have a "clay face" like appearance. Color bands can be seen. Backgrounds can loose detail as MPEG4 highlights active subjects.

This is at best misleading and at worst blatantly wrong.

First of all, let's be clear that "MPEG4" refers to a whole family of standards, including MPEG4 Part 2 (ASP) which is used in (among other things) Xvid. To my knowledge, all broadcasting uses of "MPEG4" use MPEG4 Part 10 (AVC / H.264) which is an entirely different compression standard.

The H.264 standard does not say that the encoder has to highlight active subjects, or that it should blur the image.

The reason you sometimes see these problems in H.264 is because of crappy encoders. Encoders that are optimized for quality metrics like PSNR generally end up overusing the deblocking filter because it improves the score. It also ends up destroying fine detail. Similarly, many encoders have poor ratecontrol and end up blurring the crap out of the background because they don't spend enough bits on the I frame.

H.264 has many, many more options than MPEG2 and there are a lot of traps that encoders can fall into. But even the crappiest H.264 encoder beats the pants off of the bet MPEG2 encoders at the same bitrates.

The reality is that Comcast is cramming 3xHD into a 6MHz 256QAM channel (~40Mbps) which is nowhere near enough with MPEG2. As soon as there is any sort of significant motion it turns into block city. At the same bitrates, H.264 with a half-decent encoder looks fine.

Go look at the output of x264 with sane presets and then come back and tell me that H.264 has "horrific side effects".

I'm not going to claim that H.264 is somehow magic. It cannot make 6Mbps U-Verse H.264 look as good as 20Mbps MPEG2.

Lincroft, NJ

A pair of recent articles on the Multichannel News site about some more TV services moving to MPEG-4 for ("regular") HDTV:

Discovery Starts MPEG-4 Migration For Five HD Services
Animal Planet, Science in First Phase; Discovery, TLC and Planet Green to Follow in Fall
By Todd Spangler, Multichannel News - April 11, 2012

Motorola Next-Gen Transcoder IRD Ready For 'Full HD'
DSR-6000 Family Scales Up to Four Channels, Supports 1080p HD
By Todd Spangler, Multichannel News - April 12, 2012

Mike Wolf

Beachwood, NJ

I hope the customer owned equipment like TiVo and stuff will be able to support and benefit from this.