Linked by Thom Holwerda on Wed 14th Nov 2012 22:12 UTC
Internet Explorer "In Windows 8, we reimagined the browser with IE10. We designed and built IE10 to be the best way to experience the Web on Windows. With the IE10 Release Preview for Windows 7 consumers can now enjoy a fast and fluid Web with the updated IE10 engine on their Windows 7 devices. The release preview of IE10 on Windows 7 is available for download today."
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RE[9]: IE10 still disappointing
by lemur2 on Sat 17th Nov 2012 06:56 UTC in reply to "RE[8]: IE10 still disappointing"
lemur2
Member since:
2007-02-17

" They won't be equally-sized files, WebM gives slightly smaller filesizes for the same bitrate and resolution.


Am I misunderstanding something: how do you get different filesizes for the same bitrate? Bitrate is bits/time, for the same clip (time) you should get the same filesizes, modulo some header information for the codec.

What those graphs are describing are how the bitrate corresponds to the quality for a given profile. If you take the graphs as a whole they tell you how your quality will increase as you increase the filesize (bitrate) for a given clip, cheers.
"

http://en.wikipedia.org/wiki/Variable_bitrate

"Variable bitrate (VBR) is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate (CBR), VBR files vary the amount of output data per time segment. VBR allows a higher bitrate (and therefore more storage space) to be allocated to the more complex segments of media files while less space is allocated to less complex segments. The average of these rates can be calculated to produce an average bitrate for the file.

MP3, WMA, Vorbis, and AAC audio files can optionally be encoded in VBR. Variable bit rate encoding is also commonly used on MPEG-2 video, MPEG-4 Part 2 video (Xvid, DivX, etc.), MPEG-4 Part 10/H.264 video, Theora, Dirac and other video compression formats."


The better the VBR compression, the higher the average bitrate can be stored within the same filesize.

WebM has better compression for relatively slow-moving video, such as this one:

http://www.youtube.com/watch?v=rLxQiI8c1Bs

If WebM dedicates the same number of bits to such a clip as H264, the still frames captured from the WebM rendered video playback will be sharper and better quality than H264.

In areas and segments of high motion, WebM throws a lot of data away, and when you look at a still frame, whatever part of the picture is moving quickly will be rendered as a blur. H264 will be sharper, but it will exhibit artefacts. This gives WebM a poorer score in objective measures such as PSNR, but since the human eye sees high motion as blur anyway, subjectively it looks fine.

Cheers.

Edited 2012-11-17 07:12 UTC

Reply Parent Score: 1

saynte Member since:
2007-12-10

How can you have a "higher average bitrate" within the same filesize?

It's like saying you and I both ran a marathon (filesize) in the same amount of time (clip running time), but you went faster.

One average bitrate can't be higher than the other for a clip of the same length and filesize; they are the same.

As to your other point: so you have no benchmarks (even screenshots?) to support your claim that WebM has higher quality/bitrate than x264? Okie.

Edited 2012-11-17 07:34 UTC

Reply Parent Score: 3

lemur2 Member since:
2007-02-17

How can you have a "higher average bitrate" within the same filesize?

It's like saying you and I both ran a marathon (filesize) in the same amount of time (clip running time), but you went faster.

One average bitrate can't be higher than the other for a clip of the same length and filesize; they are the same.


With VBR, AFAIK the bitrate refers to the video as rendered, not the video as compressed. Because WebM static compression quality per bit is better than h264, and because most video is lower motion rather than higher motion, WebM can deliver a higher (as rendered) bitrate from the same number of as-compressed bits.

As to your other point: so you have no benchmarks (even screenshots?) to support your claim that WebM has higher quality/bitrate than x264? Okie.


Where WebM suffers in terms of objective measurements is in areas of high motion. Because WebM (deliberately) blurs these high dynamic areas, so as not to waste too many as-compressed bits, they compare very poorly between the rendered still frames and the original still frames, and cause WebM to score poorly on objective measures such as PSNR, even though to the human viewers eye when watching the video at normal speed, the blurring of high motion areas has little detrimental (objective) effect on the as perceived quality.

Due mostly to the blurring of high-motion video, a real-life WebM video can easily be objectively measured in terms of YSSM and PSNR as being lower quality than an h264 video, yet still preferred objectively by a human viewer watching the video at normal playing speed. In addition, if you take a still of the same frame during a low-motion scene from WebM and H264, the WebM still frame will be distinctly clearer and sharper, but on some other frame during a high-motion scene, the H264 still frame will be far cleaer and sharper than the WebM one.

So the perceived quality and the measured quality can be quite different.

I did have some screenshots of this which illustrated the point very well, but I can no longer find them. Sorry about that.

I am not, BTW, claiming that WebM is better than H264. I am merely claiming that it performs differently, and for the purposes of video over the web, just as well as h264.

Edited 2012-11-17 10:24 UTC

Reply Parent Score: 1