Discrete HTPC GPU Shootout

We will now devote a couple of sections to open source / freeware software for HTPCs running Windows 7.

One of the main issues with the integrated GPUs in the Clarkdale/Arrandale and Sandy Bridge CPUs is the fact that the Intel HD Graphics engine doesn't play nice with open source software. Commercial Blu-ray playback software have woeful support for MKVs and HD audio bitstreaming from non-Blu-ray sources. Users of the Intel IGP are often left to implement a series of hacks (such as using the Arcsoft and Cyberlink decoders in other DirectShow players) to get the expected HTPC experience.

Windows 7 uses the DirectShow / Media Foundation framework for media processing. A detailed description of the framework is beyond the scope of this piece. However, what we need to specifically be aware of is the architecture of the DirectShow framework, as described here.

The two important components of the filter chain in the above link are the splitter and the decoder. MPC-HC is undoubtedly the most common DirectShow based media player used to playback HD material. The player aims to make the task of the filter construction transparent to the user by packaging a variety of source filters for various containers. These include the Gabest MPEG Splitter, internal Matroska Splitter (I remember preferring the Haali Matroska Splitter from the CCCP codec pack in late 2009), MP4 Splitter, OGG Splitter etc. A look at the standalone filters reveals the large number of standalone source filters / splitters which are in the self-contained executable.

It is preferable to have a single actively developed multi-format splitter capable of handling a wide variety of containers with a multitude of audio and video codecs / subtitle formats. This is where the LAV Splitter project comes in. Basic supported for decrypted Blu-rays (playback of MPLS / index.bdmv files) is the icing on the cake.

With HD audio capable AV receivers becoming the rule rather than the exception, one increasingly finds users interested in HD audio bitstreaming. MediaSmartServer's Damian has a great guide dealing with the usage of ffdshow for HD audio bitstreaming. Advanced users often consider ffdshow Audio as bloatware for those who just want HD audio bitstreaming. LAV Splitter comes with the optional LAV Audio Decoder which achieves the same purpose. For users who want HD audio to be decoded in a bit-perfect manner, the LAV Splitter can also connect to the Arcsoft Audio Decoder as explained here. In this section, we will deal only with HD audio bitstreaming.

The gallery below shows the sequence of steps to install LAV Splitter and Audio Decoder on a Windows 7 machine for usage with MPC-HC. You can also use any other DirectShow based player. The LAV Audio Decoder is then configured to bitstream all the HD audio formats.

Ensure that all the file formats chosen in screenshot 5 are unselected in screenshot 8 (MPC-HC options -> Internal Filters -> Source Filter). Also, the Transform Filters for AC3 and DTS must be unselected to ensure that the LAV Audio Decoder is used. Screenshots 9 through 12 show the setting up of the LAV Audio Decoder for bitstreaming in the External Filters section using the 'Add Filter' button. Screenshots 13 through 16 show the setting up of the LAV Splitter in a similar manner. Fortunately, the default settings in the splitter configuration are good to go unless you have some specific requirements with respect to the language code or don't want the LAV Splitter to activate for some specific extensions. Make sure that both the LAV Splitter and the LAV Audio Decoder are set to 'Prefer' in the External Filters section.

Playing back interlaced VC-1 clips with the default codecs in MPC-HC usually results in a blank screen. To resolve this, the Arcsoft Video Decoder needs to be registered and used. (The WMV Decoder DMO codec is able to play back such clips, but it does software decode). After installing Arcsoft TMT (TMT 5 was used to test this out), the Arcsoft Video Decoder (ASVid.ax) was manually registered using the regsvr32 command in Administrator mode. This exposes the decoder for inclusion in the External Filters section in MPC-HC, as in the first picture of the gallery below. However, setting the decoder to Preferred doesn't enable its usage unless the checkactivate.dll from this doom9 post gets placed in the same folder as ASVid.ax. After this process, an interlaced VC-1 clip can be loaded into MPC-HC. In the default configuration, you will still end up with a blank screen. The VC-1 output compatibility of the LAV Splitter needs to be configured to reflect the presence of the Arcsoft VC-1 decoder, as in the rest of the screenshots in the gallery below. Note that this configuration is necessary only for AMD (and Intel) GPUs. NVIDIA GPUs have a open source decoder capable of playing back interlaced VC-1 clips in any DirectShow based player. We will cover that in the next section.

Once configured, you should be able to see the filters in action during the playback of any media file in the appropriate container.

Playing The DaVinci Code's BR Folder Structure - index.bdmv

(Click to Enlarge)

We have never seen the ffdshow Audio decoder successfully bitstream E-AC3 (Dolby Digital Plus). With the LAV Audio Decoder, there were no such issues.

The ease of use of the LAV Audio Decoder, its tight integration with LAV Splitter and the ability to use the Arcsoft HD audio decoder for DTS-HD / DTS-ES streams (for which no open source decoders exist) make it a very attractive option for HTPC users.