[opendtv] Re: AVC realistic bitrates?

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Thu, 9 Jun 2005 07:37:16 -0400

It is virtually impossible to judge compression quality by looking at 
still frames. For one thing, I frames will typically look better than 
B frames. And then there is the reality that the brain integrates 
across multiple frames, so the nature of the degradation from 
compression will be different depending on the tools used by the 
encoder. My educated guess is that the lower bit rate AVC streams may 
actually look better than the higher bit rate MPEG-2 streams, despite 
being a little softer.

The point is that one cannot make judgements like this without 
considering the whole, not just the best parts...

Regards
Craig

At 12:26 PM -0400 6/8/05, Manfredi, Albert E wrote:
>Kon Wilms wrote:
>
>>  Instead of guestimates, try this for size:
>>  http://www.xile.net/xvid_vs_x264/720p.html
>>
>>  With a tweaked mencoder/ffmpeg script I am encoding
>>  @ 2500-3000Kbits for Divx5-HD (reduced to 960x540)
>>  and AVC (720p) with great results.
>>
>>  This is using the open source x264 AVC codec BTW.
>>
>>  Note that Xvid with postprocessing filters can be made
>>  to look as good as the 3Mbit quicktime H264 frame (and
>>  it also soft-decodes on a 733Mhz Intel CPU, unlike
>>  AVC).
>
>Very interesting results. Ron makes an excellent point,
>though, which would affect the results in a moving image
>situation. As to a comparison of the still images,
>careful inspection shows that the MPEG-2 image at 10
>Mb/s fairly handily beats out all the others.
>
>The 3 Mb/s H.264 comes close, but falls short. The most
>obvious places to look are the guy's head and shirt in
>the left foreground, the wall up on top of the steps,
>and the trees behind that wall.
>
>With MPEG-2 at 10 Mb/s, you can see quite a bit more
>texture in the guy's hair, in his shirt, an on the wall.
>The H.264 images at 3 Mb/s are much more homogenized in
>these areas, almost looking like image blur. Especially
>so with QuikTime, which looks shiny smooth vs textured.
>
>At 1 Mb/s, all the H.264 are degraded, obviously
>mencoder being the worst of the bunch. Even without
>the mencoder blockiness, though, I immediately noticed
>the trees behind the wall had lost all their detail.
>
>Anyway, I'd say that *clearly* H.264 is not three times
>better than MPEG-2. Previous controlled test results
>had said twice as good to 50 percent better, and I can
>believe that.
>
>Bert
>
>
>
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