Topics
The
Directshow system
HTPC and DVD Region Control
Interlaced and progressive scan
material
Forced subtitles, forced trailers
and copyright warnings, and other UOPs
Playing DVDs off the hard-drive
Using a media server
Advanced DVD playback filters
Itty bitty settings
Remote control
HTPC as Personal Video Recorder
Setting up SPDIF audio
Acknowledgements
The Directshow system
DVD software on a Windows PC is based around the
Windows "DirectShow" subsystem, which is also what is
used to play video clips in WMV, MPEG, DivX, AVI etc
formats. It is worth gaining a basic understanding of
how Directshow works in order to set up your machine
optimally and to understand the errors that may arise
in practice.
Directshow is modular, so that whenever multimedia
is being displayed under Windows, several different
modules (which may be made by different vendors) are
in use. When playing a simple MPEG2 video clip, the
following modules are used:
Source file reader
MPEG2 splitter (separates out the audio and video
streams, which were combined into a single MPEG2 file)
Video decoding filter
Audio decoding filter
Video renderer
Audio renderer
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The different Directshow modules used to play a trailer ripped from DVD |
The workings of all these different modules have to
be synchronised, so that video will be fed to the
display device at the proper frame rate (24 frames per
second for film) and so that the audio will remain
smooth and in sync with the video. Since audio cannot
be speeded up (which would change the pitch) and any
tiny skips or pauses inserted in audio would be
audible as pops or glitches, Directshow's priority is
to playback the audio at precisely the correct speed.
Therefore the whole Directshow system takes its timing
from your soundcard. While this should result in
correct audio playback, it can sometimes lead to
non-smooth video playback. Almost always, the cure to
video smoothness problems is to make changes to the
audio system.
When playing a DVD, the source file reader is a
special 'DVD Navigator' made by
Microsoft (the filename is quartz.dll). The DVD
Navigator understands the complex set of codes which
operate DVD Menus, Chapters, alternative languages and
subtitles, multiple angles etc. There is also an
additional video decoding filter for the 'subpicture',
which is the part of the DVD which displays subtitles
and the clickable icons on a DVD menu.
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One of Zoom Player's many option screens: Directshow filter setup |
Because a Directshow system uses modules made by
several different vendors, it may be unstable in some
situations; in particular it is not advisable to
'Alt-Tab' away from your DVD player when it is in the
middle of operations such as spinning up or ejecting a
DVD.
HTPC and DVD Region Control
HTPCs when received from the factory are normally
region controlled devices; Windows itself includes DVD
Region Control functions allowing up to a maximum of 5
DVD region changes before the region becomes
permanent. Most HTPC owners by-pass region control
using one of several DVD region-free software
packages, of which the best known is
DVD Region Free
although others may be less expensive. Old-timers
still use the freeware DVD Region Killer, having first
'flashed' their DVD-ROM drive to make it a region-free
(RPC-1) drive;
DVD Genie
is also propular with some users as it allows the PC's
DVD region to be changed temporarily on a per-disk
basis.
Interlaced and progressive scan material
PCs are progressive-scan devices, in other words they
process a whole video or film frame as one continuous
block. Standard TVs (and video cameras) are interlaced
devices, in other words each video field contains only
half the video information - alternate lines are
scanned, first the odd lines and then the even lines
in the next field, but because the phosphor coating on
a TV set has a slight persistence and the human eye
responds slowly, the stripey effect that this produces
is not detectable unless, for example, you take a
still photograph of your TV screen. Film is a
progressive-scan medium, in other words each film
frame contains the whole of the video information. But
video-source material, such as music videos, some TV
programs (but not big-budget shows such as Buffy the
Vampire Slayer or Star Trek which are shot on film),
home videos and many 'featurettes' or documentaries
found as DVD extras, are interlaced because they have
been filmed using TV cameras. The consequence of this
interlacing is that there is a 30 millisecond delay
between filming the odd lines and the even lines of
each full video frame, so that if the subject matter
is moving, or if the camera is moving or panning or
zooming, then the subject matter will have changed
position between the odd lines and the even lines. To
see what this actually looks like, play any
video-source DVD (such as a music video) on your HTPC,
and in the DVD software set the deinterlacing method
to 'Weave'.
Interlaced source material is not a problem so long as
it is played back on an interlaced display such as a
TV set. However it is a perpetual problem for
progressive-scan devices such as PCs and digital
displays such as projectors, LCD and plasma. The
playback device has the choice of either displaying
exactly what is stored on the DVD, which is the
'Weave' deinterlacing method which produces the
characteristic ugly fringed effect whenever there is
motion in the image, or of applying some type of
processing to deal with this. One standard 'cheat' is
to display the material on the PC at half resolution,
so effectively displaying only the odd lines of the
video image and throwing away the troublesome even
lines - this is what most software that comes with
consumer video cameras does: a pointer to this is that
video image displayed on the PC only has 240 lines of
resolution at native resolution instead of 480 lines
as it should.
There are several types of processing which may be
used to de-interlace interlaced source material on a
PC, and it is still a developing area. Many good
consumer DVD players or display devices incorporate
Faroudja DCDi processing which is very acceptable to
most people although it produces a slightly soft video
effect which serves to cover up any residual faults
from the de-interlacing. Faroudja DCDi processing is
not an option for HTPC users since the de-interlacing
has to be done inside the HTPC (thus Faroudja DCDi is
an unnecessary feature of a display for HTPC users
unless they will also be connecting other video
sources to it). Most PC DVD software features 'Bob'
de-interlacing which usually produces better results
than 'Weave', although it can sometimes result in a
blurred effect which is identical to
PAL/NTSC
ghosting. WinDVD in all versions since
WinDVD 4 Pro has featured advanced de-interlacing
which is very much superior to either Bob or Weave,
and in many cases better than Faroudja, so that when
using WinDVD in this mode all interlacing artifacts
disappear and perfect results are produced. For this
reason WinDVD (or an alternative front-end using the
WinDVD video filter) is the recommended DVD software
for playing any interlaced source material. Some
competing software now also offers adaptive
de-interlacing or motion compensated de-interlacing.
ffdshow features an excellent motion
compensated de-interlacing filter named TomsMoComp
after Tom Barry who wrote it.
Note that all material on DVDs is strictly
speaking stored on the disk in an interlaced format
since DVD uses the NTSC or PAL TV standards which are
interlaced. However film-source material has no motion
between the two video fields containing the odd and
the even lines of the image - therefore this is
referred to as a progressive-source DVD (the DVD
format provides for a progressive-scan "flag" which
the DVD author should set for such material to help
DVD players identify it, although good quality PC DVD
software does not require this flag to be correctly
set).
Forced subtitles, forced trailers and copyright
warnings, and other UOPs
Many commercial DVDs use the 'User Operatation
Prohibited' function to provide such irritating
'features' as: non-removable subtitles, subtitles or
languages which cannot be changed in mid-movie,
trailers and copyright warnings which cannot be
fast-forwarded or skipped. Although highly irritating
for users, the authors of these DVDs continue with
such practices because they can. An HTPC can sidestep
these irritations in one of three ways: (1) once a
disk has played through the forced trailers once, the
PC can be set to commence playing the disk every time
from a later point, such as the first frame of the
actual movie; (2) software such as
DVD Idle (which
may be bundled with DVD Region Free) can eliminate
UOPs entirely, so that nothing is forced; (3) most
packages which copy DVDs to the hard drive also remove
all region protection and UOPs automatically.
Playing DVDs off the hard-drive
Most PC DVD software, in particular Zoom Player,
operates equally well whether the DVD data that it is
reading happens to be stored on the DVD-ROM drive
(e.g. drive D:) or the hard-drive (drive C:). This
opens the possibility of copying entire DVDs onto the
hard-drive. Apart from the limited DVD piracy
possibilities (this site does not support DVD piracy:
if you don't want to buy a disk then at least rent
it), reasons why a user might want to do this are:
(a) slightly quieter operation as the DVD drive is not spinning;
(b) no layer change;
(c) battery saving for laptops, e.g. for long journeys;
(d) complete elimination of region controls and 'forced subtitles';
(e) possibility of adding custom subtitles;
(f) possibility of merging two DVDs into one seamless file (e.g. both disks of Das Boot, Lawrence of Arabia or one of the Lord of the Rings extended editions, or any 'flipper' disk).
For example, the shareware program
DVDShrink can back up a DVD to hard-drive exactly as it is found on disk, but automatically eliminating region controls and forced subtitles, forced FBI warnings and other UOPs (User Operation Prohibited commands).
Alternative subtitle tracks for many movies can be found
online, or you can make your own. More information on the software necessary to do this can be found at
www.doom9.org.
Using a media server
In this context a media server is a machine with
plenty of hard drive space (typically four 250Gb
drives or more) located in a different room from your
HTPC and linked by a network (100 MBit/s is
recommended). It needs to be in a different room
because a machine with four or more hard drives
requires plenty of cooling fans and will be noisy. The
hard drives are used to store copies of CDs and DVDs.
Software is available for cataloguing these media and
for displaying cover images. The HTPC reads the
desired CD or DVD movie over the network. The user has
access to his entire DVD collection, or at least the
heart of it, without having to leave his armchair, and
without the risk of physical damage to the disks.
Most media server users choose to use desktop
alternative / DVD launcher software such as
MainLobby.
Advanced DVD playback filters
Most experienced HTPC users use one or more of the
following Directshow filters to achieve video nirvana:
AC3 filter,
ReClock audio renderer; and
ffdshow post-processing filter. All of these must
be used in conjunction with another DVD video playback
system such as Zoom Player with appropriate DVD
filters. The functionality of these add-ons is as
follows: AC3 filter and ReClock usually lead to better
handling of the audio side of things which, as
explained, should result in smoother video playback;
AC3 filter allows the audio track to be advanced or
delayed by milliseconds for perfect sync with video
(which may otherwise be a minor problem on some
systems); these filters can also perform pitch
correction for PAL movies if desired.
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Reclock in operation: here SPDIF ('AC3 passthrough') is in use so the user has chosen to use the audio card's clock as the reference clock for Directshow - that does not make use of Reclock's full functionality |
ffdshow provides
many video post-processing functions equivalent to a
multi-thousand dollar professional video processing
unit, including noise reduction, video sharpening,
de-interlacing and fine colour and gamma adjustments -
it is also a versatile set of filters which can be
used for playback of MPEG2, MPEG4, DivX and DV format
video files. If your processor is fast enough, ffdshow
should be set to perform its video post-processing
functions after having resized your video to final
display resolution. An excellent and comprehensive
beginners guide to using ffdshow for DVD playback on a
high resolution HTPC system can be found
here.
Itty bitty settings
For smooth DVD playback, the following settings are
recommended:
* Enable DMA for your DVD drive (usually enabled for
DVD drives
automatically) - in Windows XP this is done in
Device Manager/Primary (Secondary) IDE
Channel/Advanced Settings where 'Transfer Mode' should
be set to "DMA if available".
* Disconnect any network card you have, alternatively
use your HTPC on a small 'quiet' network with only one
or two other machines so that HTPC processing is
interrupted as little as possible by network activity
*
Disable as much startup and system tray software
as possible, in particular all 'scheduled tasks'
applications. Consider disabling your anti-virus
software if you are sure your system is clean.
* If using Zoom Player, set Thread Priority to 'High'
(Advanced Options/Values and Tools/Other/Player Thread
Priority).
* If using Windows 98 or Me, increase your system
cache memory for DVD reads by following the
instructions
here
under the heading Max Cache Speed - this setting is
not necessary or advisable for Windows XP users.
* For Windows XP, try some of the other performance
boosts suggested
here
* If using ffdshow with Sonic filters (or Theatertek),
you need to edit the registry to find a key in
HKEY_LOCAL_MACHINE\SOFTWARE\Sonic\CineMaster DS
DVD\2.5\VideoDecoder called "AllowAllRenderers" and
set it to 1. Try a Google search for "AllowAllRenderers"
to find other discussions of suggested registry
settings for the Sonic filters.
* If using PowerDVD 4 (or its filters under Zoom
Player), you may need to edit two registry keys to
activate SPDIF. For SPDIF to be active in PowerDVD,
the following two keys should have the following
values: [HKEY_CURRENT_USER\Software\CyberLink\PowerDVD]
"DSAUIF"=dword:00000004 [HKEY_LOCAL_MACHINE\Software\CyberLink\PowerDVD]
"DSAUIF"=dword:00000004
Remote control
Many remote control devices are available for HTPC. A
typical configuration is an infra-red remote control
with an infra-red sensor which plugs into a USB
socket, and this arrangement is inexpensive, typically
costing around $30-$40. Enterprising individuals have
used an IRDA-compatible remote control with the
infra-red reader built-in to most laptops. Mac owners
can obtain software which allows them to use a
Bluetooth mobile phone as a remote control for the
Mac, although this author is not yet aware of any PC
equivalent. Another option could be simply to use a
small wireless keyboard.
The remote control is used with software which
mimics keypresses when the buttons on the remote
control are pressed. There are several PC Remote
Control packages; many HTPC users use
Girder.
HTPC as Personal Video Recorder
An HTPC with a large hard disk makes an excellent PVR.
It requires hardware to receive the TV images - this
may either be a simple PC TV card (in which case it
might only be able to record live TV) or it may be a
more expensive 'video capture' card which can digitise
the image from any video source connected to it.
Different PC TV cards offer varying degrees of
quality, although cards manufactured by Hauppage are
among the most popular.
Advanced users use a PC with an HDTV capture card
such as that made by FusionHD. This results in a PVR
for HDTV, which is not otherwise a readily available
consumer device at present - this probably represents
the apogee of HTPC functionality. A fast processor and
a prodigious quantity of empty hard disk space are
required; the results are said to be very rewarding.
Setting up SPDIF audio
SPDIF (or sometimes S/PDIF) is the name given to the
digital audio connection between a PC and an external
receiver, amplifier or 5.1 speaker system. SPDIF is
essential for an HTPC unless either you have a 6
channel audiophile soundcard in your PC (in which case
you can connect the soundcard's outputs directly to
power amps/loudspeakers), or unless you are willing to
accept 2 channel audio which is achieved simply by
connecting your PC's headphones output to your stereo
amplifier using a suitable lead (or preferably an
inexpensive external PC stereo audio adapter which is
recommended for increased sound quality).
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A laptop port replicator: note the white DVI connector, and the SPDIF connector on the right - this is a standard RCA (coaxial) hi-fi style connector |
The SPDIF connection is physically the same as the
digital connection between a CD player and an
amplifier, also known as Toslink if optical cabling is
used. But apart from setting the correct display
resolution, setting up your HTPC to use the SPDIF
audio output is likely to be the most difficult task
for a novice user. SPDIF features on PCs are not well
documented because few people use them. In order for
SPDIF output to work, the following elements must all
be in place otherwise you will just hear silence:
* The DVD must be using a multi-channel soundtrack
(including DD2.0, but not PCM stereo tracks or MPEG
audio)
* The DVD software must be set to output SPDIF -
before using Zoom Player, try simply making the
standard WinDVD or PowerDVD software output audio in
SPDIF mode
* If using ReClock or other audio-post processing, it
must be set to a mode compatible with SPDIF
passthrough
* Windows must be set to output 5.1 channel sound and
to enable SPDIF - use Adjust Audio Properties (right
click the loudspeaker icon in the taskbar)
* Your audio adapter's drivers must support SPDIF -
early driver versions (in particular for laptop sound
systems, where SPDIF is used very rarely) may not have
activated SPDIF functionality
* The SPDIF output on your PC must be physically
connected to a digital input on your amplifier or
receiver - initially, try using a short run (no more
than 5m/15 feet) of standard RCA audio extension lead
* Your amplifier or receiver must be able to recognise
the input signal as DD5.1 (also known as AC3) or DTS
as the case may be.
If you have a problem, try to isolate it by reference
to components known to work - for example, check that
your amplifier and audio system is correctly set up
for SPDIF by connecting the digital audio output on a
standard consumer DVD player; try a standard DD5.1
track before something like DTS; if using Zoom Player,
use it with the ReClock audio renderer which has the
useful function of displaying the format of the audio
it is being fed: if ReClock is receiving SPDIF it
describes it as "Audio stream: AC3 passthrough, 48000
Hz". Zoom Player is awkward switching to SPDIF (using
the 'External' tab in Advanced Options) if using
WinDVD or PowerDVD audio filters, especially when Zoom
Player is used following the standalone WinDVD or
PowerDVD players. It may be necessary to edit Registry
entries to correctly enable SPDIF in WinDVD or
PowerDVD under Zoom Player.
The author gratefully acknowledges the help of
Matt and all at
SeeingThings.co.uk.
Feedback on this article (errors, additional HTPC
tips) can be sent to
HTPCfeedback@yac.ndo.co.uk but please do not ask
for advice about your own setup as such questions will
not be answered - instead use the online forums for
that.
All trademarks are acknowledged. Discussion of or
linking to a product does not indicate a DVD Beaver
endorsement of that product, nor that that product is
necessarily the best in its class - links are intended
only to provide examples of the types of product that
may be available, in order to help the reader with his
own further research.
