[maemo-developers] N800 & Video playback

[From: Daniel Stone]

Hi,

On Sun, Mar 18, 2007 at 07:57:36PM +0200, ext Siarhei Siamashka wrote:
> If we look at the framebuffer API. There are two ioctl important for screen
> updates and tearing synchronization if I understand them correctly now:
> 
> [...]

You do indeed understand them correctly.

> Looks like graphics bus on N800 is 3x slower than on Nokia 770. It might 
> be caused by inefficient framebuffer driver implementation in its initial
> revision. But if it is a hardware issue, getting normal video playback at
> native framerate may be troublesome. Performing software downscaling of 
> video before sending data to the graphics chip may be a solution, but it
> sacrifices image quality. Switching to 12bit YUV format from 16bit will save
> ~33% of bus bandwidth, but it can't compensate 3x performance regression 
> and may be not enough for 30 fps fullscreen video playback.

Unfortunately, it's a hardware issue.  What we can do is get the LCD
controller to perform colourspace conversion from a custom planar format
('YUV420') and the scaling as well.  Unfortunately this isn't a
colourkey, but only a simple rectangle, so the semantics are actually
quite complex.  But it works well enough that we've shipped an X server
and kernel with this support.  We've tried jacking the RFBI frequency up
a bit, and the most we could get was a ~10% improvement, with a loss in
stability: anything above that would kill your device quick smart,
whereas this one only crashed it every day or so.

> As Daniel explained, the next firmware will bring a big improvement in this
> area. I'm not sure whether it is worth to release the next version of MPlayer
> before that, since it will still be far from perfect on N800.

I'd hold your breath, to be honest.

> A preview of the next kernel for beta testing might reduce time needed to get
> MPlayer fully working on N800, but I'm not demanding or expecting anything. It
> is just a matter of time anyway and I'm not so impatient :)

Unfortunately, again, it's not my call: there are various processes to
get things released (legal, in particular), and I can't really pre-empt
those.

> I would be grateful for any comments and corrections. Some things are not 
> yet clear to me, figuring them out myself is just a waste of time that could
> be spent on something more useful. Even a small hint may save a huge 
> amount of time.

Anything in particular?  I thought my last mails on the subject would've
been reasonably exhaustive.

> PS. The last 'inefficient' period of time was when I was struggling with
> gstreamer API (with no prior experience with it) to get MP3 playback in
> MPlayer working on DSP for a few months. Looks like the history repeats. 
> Once again, I'm not demanding anything, it is just a matter of 'optimizing'
> development and spending scarce amounts of spare time more efficiently.
> I know that Nokia developers are too busy with their primary work, and
> really appreciate what they are doing. So consider this as a polite request 
> for a favour (not necessary to fulfil right now or fulfil at all).

Again, if there are any particular questions I can answer, don't be
subtle: ask me straight up.  If I can answer them (some things I can't
necessarily say, some things I don't necessarily know), I will.

Cheers,
Daniel
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