Video Acceleration and power use when playing video.

Nils Faerber nils.faerber at kernelconcepts.de
Sun Jul 8 02:20:34 CEST 2007


Ian Stirling schrieb:
> As I understand it, the chip under consideration will not decode audio.

Well, this does not matter that much.

> This essentially means that the CPU can not usually be slowed down, as
> it is required to decode MP3 audio or many other formats.

Why not?
Decoding audio needs lot less CPU resources than video so I would
estimate that the CPU can be slowed significantly. But even then there
are other problems that migh prevent CPU slow down like hvaing to feed
the decoder with data, which usually is done through the CPU which needs
to read the data from some storage, probably demux the stream and pipe
it into the decoder.

> This basically means that there is very limited power saving if any
> possible, compared to simply doing it all in the CPU.

The CPU will use a lot less cycles for decoding the video. If power
saving is your concern then it might as well help.

> Of course, it will make more video able to be decoded, without transcoding.

Right, and with much higher quality.

> On some personal tests, I found on a 2.8" screen, mpeg1 video at 120*160
>  and 300kbits/s worked just fine, which means that the only benefit this
> may have in terms of playback is if you want to have more than ~5
> hours/gigabyte, using more advanced video encodings that the CPU can't
> do, or larger video than is actually visually needed, for playback on
> other devices.

Uhh... 120*160 is pretty bad resolution :(
With an active decoder this could quite easily be QVGA or even full VGA
at full framerate. And this *is* a benefit IMHO...

Cheers
  nils faerber

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