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

[Galen]

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.

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)

2) Harness the power of my graphics card better

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)

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

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.

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...

-Galen

On Dec 3, 2004, at 11:46 PM, Benjamin PRACHT wrote:

> On Fri, Dec 03, 2004, Galen wrote :
>> I'm using VLC to play back .ts files, typically 1080i HDTV MPEG-2. I'm
>> having performance issues though. Under my configuration, I cannot get
>> the video to smoothly play. The current video playback is very jerky,
>> although the audio is fine. I would like to be able to play back the
>> video smoothly.
>>
>> This is my configuration:
>> Mac OS X 10.3.6 - 100% up to date
>> PowerBook G4 15"
>> 	1.33 GHz G4 (512 KB L2 cache)
>> 	768 MB RAM
>> 	ATI Radeon Mobility 9700 64 MB VRAM
>> 	1280 x 854 display (built-in LCD)
>>
>> I'm willing to recompile, tweak, hack, whatever. Optimally I would 
>> like
>> to get playback smooth from the .ts files. Just give me some direction
>> with what to try, that's all I need...
>>
>
> Well, HDTV streams have always required quite a big CPU for decoding,
> and I've never seen such a stream played fine on a G4... I don't think
> recompiling VLC will help (all the available optimisations of VLC are
> already included in the standard binaries). VLC uses limpeg2 for mpeg2
> decoding, which is considered as a fairly efficient mpeg2 decoder, and
> include some altivec optimisations as well. On the other hand, there
> is certainly still some room for optimisation in VLC's code (debugging
> the OpenGL vout would be a start), but this would require some time and
> skills, and I'm not sure even would allow playback of HDTV streams on a
> G4. BTW, such streams play fine on G5 cpus...
>
>
> -- 
> BigBen
>
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