iPod touch video codecs and battery life

[zen.state]

Hey all,

Just got myself an ipod touch. I was wondering if you all think that h.264 video uses more battery than regular MPEG4 (FFmpeg)?

It stands to reason that it would because h.264 is more of a CPU hog than FFmpeg. h.264 looks better for sure on large screens but on my touch it makes little difference if the original source is good quality.

Thoughts?

 

[goosnarrggh]

Hey all,

Just got myself an ipod touch. I was wondering if you all think that h.264 video uses more battery than regular MPEG4 (FFmpeg)?

It stands to reason that it would because h.264 is more of a CPU hog than FFmpeg. h.264 looks better for sure on large screens but on my touch it makes little difference if the original source is good quality.

Thoughts?

The iPod Touch has a hardware-accelerated h.264 video decoder; the CPU burden of watching h.264 video is quite small. In fact, any other compressed video format which cannot use the h.264 hardware acceleration would eat up substantially more power.

 

[zen.state]

The iPod Touch has a hardware-accelerated h.264 video decoder; the CPU burden of watching h.264 video is quite small. In fact, any other compressed video format which cannot use the h.264 hardware acceleration would eat up substantially more power.

The decoder still needs to run off battery power my friend.

Logic tells me that the less hardware you are using in the touch the less battery it would use.

 

[goosnarrggh]

The decoder still needs to run off battery power my friend.

No argument there.

Logic tells me that the less hardware you are using in the touch the less battery it would use.

Without some more facts, there is not enough information to draw that conclusion.

It turns out that the total energy consumed (CPU + accelerator) to decode a video using a dedicated video decoder can actually be less than the total energy which would have been consumed to do the same job in a general purpose CPU alone using software only. This is probably because the accelerator's circuitry has been specifically optimized for the task of decoding video.

The CPU time which would otherwise have been spent decoding the video might instead be spent by the iPhone OS doing other tasks, or the CPU frequency might be scaled back to a much lower frequency, or the CPU could simply be put to sleep between setting-up DMA transfers.

Studies have been performed which confirm these predictions.
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