[Theora] Playback too slow?!

[Alen Ladavac]

Hi Ivan,

I am very interested in these "decode-efficient" encoding parameters. I have
a bunch of movies in 640x480, 30fps that would need to be decodeable on a
733MHz Celeron. If you have some suggestions on how to encode that to double
the decoding speed, I'd be very grateful. :)

What is this theora-encoder you are using, and what those parameters mean? I
have searched the entire svn repository for text "hqdn3d", but haven't found
any. So I'd guess this is not the theoraenc, is it?

Thanks,
Alen


----- Original Message -----
From: "Ivan Popov" <pin at medic.chalmers.se>
To: "Ole Tange" <tange at tange.dk>
Cc: <theora at xiph.org>
Sent: Wednesday, March 30, 2005 08:46
Subject: Re: [Theora] Playback too slow?!


> Hi Ole,
>
> On Wed, Mar 30, 2005 at 12:46:59AM +0200, Ole Tange wrote:
> > > theora-encoder -va -vf -va crop=704:424,scale=528:320,hqdn3d=4:3:6 \
> > >                -s 64 -S 45 \
> > >                -a 0 -v 5.4 -o 528-320-5.4-0-436.ogg \
> > >                dvd://1
> >
> > How do you detect these values?
> >
> > I guess 704:424 is from 'mplayer -vf cropdetect'. 528:320 and 4:3:6 is
> > probably your own idea though it is not clear to me why you chose
> > precisely these values. But where do -s 64 -S 45 come from? What I am
>
> well, it is not exactly easy...
>
> 64/45 came from the dvd movie itself - that is the aspect ratio of the
pixels.
> Looking at mplayer output while playing the movie you see what is
> "pixels x pixels" size and what is the right picture aspect, then you want
to
> recalculate that to "pixel aspect" which theora uses.
>
> Those numbers (sadly) vary from movie to movie, according to the choice
> of the manufacturer. You can have all from square pixels to very wide
> or tall.
>
> >>That test transformed 122 minutes of DVD 1001x424 (really
720x424=>1024x424)
>
> That particular movie (excluding the extra black areas) has the aspect
ratio
> about 2.4, while it is coded as 720x424 pixels, so each pixel represents
> a non-quare rectangular.
> I deliberately crop it to the more standard 2.35 aspect ratio,
> keeping the pixel aspect intact. So crop visible 1024->1001 means
> crop internal 720->704.
>
> >>into 670 MB of 750x320 (really 528x320) which my 800 MHz Athlon can play
> >>without frame drops.
>
> I chose to keep the pixel aspect ratio intact, to avoid extra
interpolation.
> Then I scale down the resolution to both reduce the resulting file size
> and ensure that my hardware can cope with it in real time.
>
> So, 704x424 representing about 1001x424 on the screen became
> 528x320 representing about 750x320.
>
> In contrast, ffmpeg2theora converts the image to square pixels before
> encoding to theora. That is a more straightforward approach,
> though it introduces some minor loss in quality and also is slightly less
> efficient at encoding.
> Anyway, for both approaches you (or the program) have to know
> the "right" aspect ratio, which is not always correctly present in the
> original file (surprise :)
>
> > after is: Could these be autodetected so the normal user will not need
to
> > figure these out?
>
> Normally a program (in our case mplayer) can figure it out.
> Unfortunately mplayer uses the aspect ratio at the display level,
> not at the decoding level, so that theoraenc does not get the information
> in the yuv4mpeg stream.
>
> About the hqdn3d parameters, they should be tuned for the particular file.
> They are definitely different when I encode tv shows taken by the same
receiver
> card on different channels - as the noise level is different.
>
> The numbers above improve compression while do not remarkably influence
> the quality of a dvd source. They come from mplayer manual, I think.
>
> On some movies you want also a deinterlacing and/or
> reverse telecine filter (see man mplayer).
>
> > I am all for configurability. But if we have good defaults that give
> > excellent results in most cases then it will be easier for non-geeks to
>
> Alas, I am not aware of such defaults :) All cases are indeed very
different.
>
> One dvd movie I trancoded became 3 CDs, the first one containing exactly
> a half of the movie, and two others - one quarter each. The reason was
> that the second part of the movie contained a lot of motion and I could
> not use the same quality setting and get the same compressed size.
>
> > use theora without tweaking.
>
> Some day when the "fixed bitrate" mode will be improved, may be.
> It depends also on your preferences.
>
> > I am quite impressed with the speedup your suggestions made. From 90%
CPU
> > usage I am now around 40% - i.e no framedropping and quite usable. Thank
> > you.
>
> Thanks. You are welcome.
>
> May be I should put ffmpeg2theora on konvalo.org as well.
> It does not exactly suit my purposes, but possibly will be of use for
others.
> Stay tuned.
>
> Regards,
> --
> Ivan
>
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