What would be a realistic but challenging level for Bryce announced trophy money for video playback on the Neo1973? Re: h.264 format is now open?

[Bryce Leo]

Now there is some most promising news, sound like with some simple
optomizations for scaling that this shouldn't be too difficult eh? I
put the full post about the bounty to the Dev maliing list. but the
link to the wiki page is
http://www.linuxtogo.org/gowiki/OpenMoko/Video_Bounty
That's the current home of the full rules for the contest. Your news
is great but it's almost a shame that it looks like it'll be trivial
to do.

> A few technical questions here. Is image data constantly transferred to LCD
> from system memory (60 times per second)?
>
> If we compare it to Nokia 770, Nokia 770 has a similar design with framebuffer
> stored in the system memory with data getting transferred to graphics chip
> using DMA when needed (graphics chip has its own video memory). Anyway,
> screen update requests do not seem to have any visible impact on video
> decoding performance (tested with 640x480 24 fps video). So DMA transfers
> are not too expensive and cpu can do some other useful things while DMA
> transfer is in process.
>
> If video is really heavy on memory bus, is it possible to reduce refresh rate
> somewhat (to 50Hz for example) to improve performance?
>
> By the way, initially some people also considered Nokia770 hardware
> to be too slow for video playback with full fps and more or less acceptable
> quality, check built-in video player limitations [1], but now using MPlayer
> build for maemo [2], it can handle even some nontranscoded video files
> more or less successfully. For example when using the following video clip
> (http://www.divx.com/movies/detail.php?movieID=57&cID=1), it can
> be watched fullscreen with ~30% frames dropped (resulting in jerky
> playback on fast moving scenes).
>
> If we compare Neo 1973 to Nokia 770, it:
> * has ~5% faster cpu clock frequency
> * does not have enhanced dsp instructions support (these instructions provide
> ~10-15% decoding performance improvement currently)
> * does not have DSP to relay audio decoding to it (mp3 audio takes ~15% cpu
> resources if libmad decoder is used on ARM core)
> * does not have hardware YUV support (that may result in more cpu resources
> needed for video output and a lot frames dropped because of software YUV->RGB
> conversion)
>
> So while Nokia 770 should be faster for video, Neo 1973 is not too far behind.
>
> But one of the most important performance statistics is memory bandwidth, can
> anyone benchmark memcpy on copying a large data block? Nokia 770 has memory
> copy bandwidth up to 110MB/s, if Neo 1973 has a similar memory performance,
> it should be not so bad for video.
>
> Just for some experiment, I compiled mplayer for arm920t (not using armv5te
> instructions), and benchmarked it with sdl video output (software YUV->RGB
> conversion, generic nonoptimized scaling 320x240 => 640x480) and libmad
> mp3 audio decoder. This test was run on Nokia 770, but the intention was to
> simulate how it can possibly behave on Neo 1973.
>
> # mplayer -endpos 100 -vo sdl -ac mad -framedrop -quiet -benchmark test.avi
>
> VIDEO:  [DIVX]  320x240  24bpp  23.976 fps  401.2 kbps (49.0 kbyte/s)
> AUDIO: 44100 Hz, 2 ch, s16le, 128.0 kbit/9.07% (ratio: 16000->176400)
>
> BENCHMARKs: VC:  46,446s VO:  38,929s A:  13,574s Sys:   2,082s =  101,031s
> BENCHMARK%: VC: 45,9718% VO: 38,5312% A: 13,4359% Sys:  2,0611% = 100,0000%
> BENCHMARKn: disp: 1368 (13,54 fps)  drop: 1031 (42%)  total: 2399 (23,75 fps)
>
> Actually VO: part in this benchmark can be heavily optimized and video
> playback without dropping frames for this resolution and bitrate should be
> possible. Also if we badly need to watch some video at any cost and can't
> transcode it, video can be watched in grayscale, in this case video decoding
> is a bit faster and we don't need resource consuming YUV->RGB conversion
> (conversion to grayscale is cheap).
>
> Anyway, let's wait for the information from the first Neo 1973 owners. I think
> that the information about real Neo 1973 multimedia capabilities will be
> available really soon :)
>
> [1] https://maemo.org/maemowiki/VideoEncoding
> [2] https://garage.maemo.org/projects/mplayer/
>
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