libvpx works on Sega Dreamcast

[Mike Melanson]

I'm sure I'm the only person who could possibly care about this (and I
don't even care that much), but I managed to get libvpx 0.9.5 ported to
the Sega Dreamcast game console (Hitachi/Renesas SH-4 CPU). It mostly
works too!

It took a little effort but nearly all of the source code compiled
as-is. So, good work with the portability. :)

--
-Mike Melanson

[Ralph Hauwert]

Agree, portability is great! How are the FPS on dreamcast ?

Ralph.

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[Alex Converse]

Mike,

Your crazy hacker spirit never ceases to amaze me. Congrats.

--Alex Converse

[Mike Melanson]

On 02/18/2011 01:09 AM, Ralph Hauwert wrote:
> Agree, portability is great! How are the FPS on dreamcast ?

Hard to say at this point. So far, I have only ported the
decode_to_md5.c utility so that I can test bit exactness via a serial
console. I haven't hooked the decoder up to the video output yet.

The decoder does crash after enough frames. I haven't delved into the
'why' yet. I was just startled to see correct MD5 sums start pouring out
of the console.

I wouldn't expect impressive FPS-- the DC struggled to play low-res
MPEG-4 part 2 video.

--
-Mike Melanson

[Ralph Hauwert]

I'm curious for sure, if you do get any results on that, would love to hear.

Furthermore, how are you planning to do yuv->rgb conversion ? Does the DC have enough functionality in it's graphics processor to do so ?

Ralph.

[Mike Melanson]

On 02/18/2011 01:28 AM, Ralph Hauwert wrote:
> I'm curious for sure, if you do get any results on that, would love to hear.
>
> Furthermore, how are you planning to do yuv->rgb conversion ? Does the DC have enough functionality in it's graphics processor to do so ?

Not directly. But there is a trick with texture blending that can
facilitate conversion:

http://multimedia.cx/yuv-3d-rgb.txt

I'll definitely try to get visual playback happening, just for fun. :)

--
-Mike Melanson

[John Koleszar]

Nice work, Mike! And for the parts that didn't, patches welcome -- we
did compile on SH-4 in the past...

[Frank Galligan]

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   -Mike Melanson

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Cool. I remember working on TM2X on the Dreamcast. That was a long time ago.

[Mike Melanson]

I suspect you did so for Linux/SH-4. This was on a custom, purpose-build
RTOS and most of the mods I made just needed to make it fit more nicely
with the RTOS' almost-POSIX-compatible system libraries.

If I get down to figuring out why it's crashing on certain frames (and
if it's truly a bug in libvpx), I'll surely send along a patch.

--
-Mike Melanson

[Mike Melanson]

On 02/18/2011 05:57 AM, Frank Galligan wrote:
> Cool. I remember working on TM2X on the Dreamcast. That was a long time ago.

Do you know if any released DC games used TM2X? The only FMV formats I
have seen on DC games are Sofdec and 4XM. In fact, the only place where
I have ever seen TM2 video remains Final Fantasy VII for PC.

--
-Mike Melanson

[Mike Melanson]

On 02/18/2011 05:50 AM, John Koleszar wrote:

> Nice work, Mike! And for the parts that didn't, patches welcome -- we
> did compile on SH-4 in the past...

Found the crashing problem: libvpx-v0.9.5/vp8/common/reconinter.c has to
#define MUST_BE_ALIGNED. In the default distribution, this is commented
out with a note that it must be enabled on such architectures as ARM.
Are ARM system integrators expected to figure this out or is there
out-of-file documentation on the matter?

Thanks...
--
-Mike Melanson

[Frank Galligan]

Yeah there were a few in Japan, not many (I don't remember right now). I also remember Toy commander and an NHL game I think.

If I run across any dreamcast disks with that shipped with TM2X I will let you know. If a disc shipped with TM they usually had  a TM logo on the back, but not always. 

--
   -Mike Melanson

[Fritz Koenig]

It varies from device to device. Earlier ARM devices we were working
required aligned reads. I believe it's something that can be set up
in configuration registers. Newer devices we were programming for did
not have this restriction.

But no, there is no other documentation, sorry.

[Fritz Koenig]

This is compiler reference from ARM[1]. Pre v6 does not support
unaligned access, post does, but must be configured.

[1]: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0491c/CIHCGCFD.html

[Mike Shaver]

On Fri, Feb 18, 2011 at 11:36 AM, Fritz Koenig <frko...@google.com> wrote:

> It varies from device to device.  Earlier ARM devices we were working
> required aligned reads.  I believe it's something that can be set up
> in configuration registers.  Newer devices we were programming for did
> not have this restriction.

Even where unaligned access doesn't trap, isn't it a significant
performance penalty?

Mike

[Attila Nagy]

On the contrary, it's a speedup on arm. No penalty!
Nice work!

[John Koleszar]

Yes.. There's a configure switch (--disable-fast-unaligned) that's
supposed to configure whether to try unaligned accesses at all, but it
looks like the functions that used to use it don't anymore. Should be
a straightforward fix to connect it here, or just change the default
behavior in reconinter.c to the safe/slow versions, since nobody's
going to use the C versions of these in production anyway.

[Mike Melanson]

I think that's generally true. Fortunately, the VP8 code usually aligns its buffers. But for motion compensation (at issue in this case), the unaligned accesses are just part of the game.

-Mike Melanson

[Måns Rullgård]

Mike Shaver <mike....@gmail.com>
writes:

One cycle compared to an aligned access.

--
M�ns Rullg�rd
ma...@mansr.com

[Mike Melanson]

On 02/18/2011 01:28 AM, Ralph Hauwert wrote:

> I'm curious for sure, if you do get any results on that, would love to hear.

Update: Realtime playback IS possible! ... if the video is 176x144 ...
and you don't do YUV -> RGB conversion (just display the Y plane) ...
and no audio decoding to go along with video playback.

:)

More details here:

http://multimedia.cx/eggs/decoding-vp8-on-a-sega-dreamcast/

--
-Mike Melanson