[vlc] Re: HDTV Transport Streams (.ts) and Performance

[Manu Abraham]

On Sat December 4 2004 4:32 pm, Benjamin PRACHT wrote:
> On Sat, Dec 04, 2004, Galen wrote :
> > I was just thinking here, what about somehow repackaging (but not
> > re-encoding) the stream to play in the Apple DVD Player? I pulls some
> > magic with MPEG2 decoding, thanks to some sort hardware assist and/or
> > amazing optimization. For comparison, my old laptop, an iBook, would
> > play DVDs perfectly with Apple DVD Player. Something like 30-40% of the
> > CPU. Yet not a single DVD would play smoothly with VLC or other similar
> > media players. Higher data rate discs and scenes faired the worst with
> > alternate players, yet not a single skip ever happened with Apple's
> > player. I've seen this phenomenon repeated over and over on many Macs.
>
> Yeah, Apple DVD player can use the hardware iDCT routines of graphic
> cards. VLC cannot do that, since we lack the specifications of these
Benjamin,

The company were i used to work earlier developed an application that 
harnesses the features of the "NVIDIA" cards. This application was on 
Windows, though an OpenGL application, if you are interested maybe i could 
give you his contact.. though i was never into the development of that, maybe 
he could give you a few pointers, if i am correct..


Manu

> hardware functions. However, these functions are fit to decompress a DVD
> stream. I doubt cards would be able to decompress a 1920x1080 4:2:2
> stream. I might be wrong, recent cards could have support for HDTV MPEG2
> profiles, but even that way, I don't think Apple DVD player would eat
> such big streams, even if authored as a DVD, without rescaling them and
> coverting the chroma.
>
> > I realize that a DVD-formatted VIDEO_TS folder with HDTV resolution
> > would be way out of spec for DVD playback, but perhaps, just perhaps,
> > it would work with the Apple player. The underlying formats are close
> > enough, I think - MPEG 2, AC3. The Radeon 9700 Mobility in my machine
> > is really pretty powerful in terms of raw function.
> >
> > Anybody have a clue to try this technique? Or am I completely and
> > utterly crazy for event thinking this? (If this is the case, please be
> > gentle...)
> >
> > If not via the Apple DVD Player, are there any other ways to harness
> > greater hardware acceleration? If the G4 won't do the trick by itself
> > with existing decoders, the solutions seem to fall into the following
> > categories:
> >
> > 1) Reduce CPU requirement through shortcuts (with a quality and/or
> > resolution cost I'm sure) or better decoders (not terribly likely)
>
> Well, I don't think standard MPEG2 streams allow to reconstruct an image
> by only decoding part of the stream.
>
> > 2) Harness the power of my graphics card better
>
> As said before, even if your card can decompress HDTV stream, we lack
> the specifications (and the probably the developpers) to implement it.
>
> > 3) Re-encode the file such that less processing is required to view it
> > - not very convenient, several hours or more for a single television
> > show as far as I can tell (without using up incredible amounts of drive
> > space)
>
> Well, this is the only way I see to play your stream... rescaling and
> reencoding it...
>
> > Now I'm wondering if it's even reasonably for me to ask my computer to
> > play back HDTV content. So to get a little perspective, let's look and
> > see what PCs require to play back HDTV streams. The pcHDTV requirements
> > (copied and pasted from their site) for playback on an x86 Linux
> > system:
> >
> > Intel® Pentium® 1200Mhz or higher
> > NVIDIA card with IDCT acceleration for machines under 2000MHz.
> > Linux Red Hat Linux 7.2, 7.3, 8.0 or 9.0.
> > Sound card with S/PDIF support and external sound system.
> > 256 Meg RAM or higher
>
> Well, it seems here that at least NVidia cards can iDCT HDTV streams...
> but again, VLC cannot use these functions
>
> > Isn't that interesting... it seems my machine is likely faster than
> > those specs given. 1333 MHz G4 CPU - should easily be faster than a 1.2
> > GHz Pentium - and people claim (with some support) that G4s are faster
> > per Mhz than P4s. Video card? I would hope a Radeon 9700 mobility beats
> > a basic Nvidia with IDCT accelation. The remainder of the specs are not
> > even competitive with my setup.
>
> Well, when it comes to video treatment, at least with the
> decoders/encoders we are using (libmpeg2/ffmpeg), my experience is that
> G4 are not really faster than Pentium III or IV... Don't forget that,
> contrary to MacOS X, linux can use overlay to display the stream, meaning
> that the chroma conversion can be done by the graphic card, and this step
> can quite CPU consuming with a HDTV stream.
>
> > Yet people running on x86 Linux can play HDTV with those specs, and my
> > machine with better specifications, cannot. It seems pretty clear to me
> > something is really wrong/broken/flawed with playback under Mac OS X.
> > Is it the OS? The decoders? Hardware acceleration (or lack thereof)?
> > What's the hang-up? My $2000 Mac laptop can't play what a $200 Linux
> > desktop off pricewatch.com can do with SETI at Home running in the
> > background.
> >
> > So before I sulk in the corner, hopelessly depressed with my computer,
> > can anybody explain the disparity? Or better yet, help me overcome
> > it...
>
> --
> BigBen

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