One of the video post processing aspects heavily emphasized by the HQV 2.0 benchmark is cadence detection. Improper cadence detection / deinterlacing leads to the easily observed artifacts during video playback. When and where is cadence detection important? Unfortunately, the majority of the information about cadence detection online is not very clear. For example, one of the top Google search results makes it appear as if telecine and pulldown are one and the same. They also suggest that the opposite operations, inverse telecine and reverse pulldown are synonymous. Unfortunately, that is not exactly true.

We have already seen a high level view of how our candidates fare at cadence detection in the HQV benchmark section. In this section, we will talk about cadence detection in relation to HTPCs. After that, we will see how our candidates fare at inverse telecining.

Cadence detection literally refers to determining whether a pattern is present in a sequence of frames. Why do we have a pattern in a sequence of frames? This is because most films and TV series are shot at 24 frames per second. For the purpose of this section, we will refer to anything shot at 24 fps as a movie.

In the US, TV broadcasts conform to the NTSC standard, and hence, the programming needs to be at 60 frames/fields per second. Currently, some TV stations broadcast at 720p60 (1280x720 video at 60 progressive frames per second), while other stations broadcast at 1080i60 (1920x1080 video at 60 fields per second). The filmed material must be converted to either 60p or 60i before broadcast.

Pulldown refers to the process of increasing the movie frame rate by duplicating frames / fields in a regular pattern. Telecining refers to the process of converting progressive content to interlaced and also increasing the frame rate. (i.e, converting 24p to 60i). It is possible to perform pulldown without telecining, but not vice-versa.

For example, Fox Television broadcasts 720p60 content. The TV series 'House', shot at 24 fps, is subject to pulldown to be broadcast at 60 fps. However, there is no telecining involved. In this particular case, the pulldown applied is 2:3. For every two frames in the movie, we get five frames for the broadcast version by repeating the first frame twice and the second frame thrice.

Telecining is a bit more complicated. Each frame is divided into odd and even fields (interlaced). The first two fields of the 60i video are the odd and even fields of the first movie frame. The next three fields in the 60i video are the odd, even and odd fields of the second movie frame. This way, two frames of the movie are converted to five fields in the broadcast version. Thus, 24 frames are converted to 60 fields.

While the progressive pulldown may just result in judder (because every alternate frame stays on the screen a little bit longer than the other frame), improper deinterlacing of 60i content generated by telecining may result in very bad artifacting as shown below. This screenshot is from a sample clip in the Spears and Munsil (S&M) High Definition Benchmark Test Disc

Inverse Telecine OFF Inverse Telecine ON

Cadence detection tries to detect what kind of pulldown / telecine pattern was applied. When inverse telecine is applied, cadence detection is used to determine the pattern. Once the pattern is known, the appropriate fields are considered in order to reconstruct the original frames through deinterlacing. Note that plain inverse telecine still retains the original cadence while sending out decoded frames to the display. Pullup removes the superfluous repeated frames (or fields) to get us back to the original movie frame rate. Unfortunately, none of the DXVA decoders are able to do pullup. This can be easily verified by taking a 1080i60 clip (of known cadence) and frame stepping it during playback. You can additionally ensure that the refresh rate of the display is set to the same as the original movie frame rate. It can be observed that a single frame repeats multiple times according to the cadence sequence.

Now that the terms are clear, let us take a look at how inverse telecining works in our candidates. The gallery below shows a screenshot while playing back the 2:3 pulldown version of the wedge pattern in S&M.

This clip checks the overall deinterlacing performance for film based material. As the wedges move, the narrow end of the horizontal wedge should have clear alternating black and white lines rather than blurry or flickering lines. The moire in the last quarter of the wedges can be ignored. It is also necessary for both wedges should remain steady and not flicker for the length of the clip.

The surprising fact here is that the NVIDIA GT 430 is the only one to perfectly inverse telecine the clip. Even the 6570 fails in this particular screenshot. In this particular clip, the 6570 momentarily lost the cadence lock, but regained it within the next 5 frames. Even during HQV benchmarking, we found that the NVIDIA cards locked onto the cadence sequence much faster than the AMD cards.

Cadence detection is only part of the story. The deinterlacing quality is also important. In the next section, we will evaluate that aspect.

Custom Refresh Rates Deinterlacing Performance
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  • qwertymac93 - Monday, June 13, 2011 - link

    What the heck are you talking about? Reply
  • velis - Monday, June 13, 2011 - link

    A great review. Provides all the answers one could wish for and even gives some further hints.
    I sure hope you have something like this lined up for llano.

    If I may suggest a couple or three things:
    Perhaps you should also mention reclock - it will solve most 23.976 and similar problems... It's not like many will detect that the video is running 1/24000th faster. Plus it's insanely easy to use.
    I understand you couldn't just post full blown images for space problems, but those thumbnails require too much work too. Is it possible to display a popup of sorts when one mouse-overs those thumbnails?
    Also a vertical line showing 60FPS in those DXVA tests would be great :)
    Reply
  • ganeshts - Tuesday, June 14, 2011 - link

    I will pass on your request(s) to the person in charge of the graphing engine :) Reply
  • Salfalot - Monday, June 13, 2011 - link

    What might have been a nice option is to see what sound levels the cards produced. Even it was only for the GT430 and the HD6570. I know that the decibels can differ between manufacturers but it would have been nice!
    For the rest a very nice detailed review between HTPC cards. I was deciding which card to buy so this helped a great deal! I was only looking between the HD6450 and the HD6570 but the GT430 is a better option than the HD6450.
    Reply
  • nevcairiel - Monday, June 13, 2011 - link

    HDMI Audio is purely digital, there is no diference based on what card you use.

    It depends on the audio decoder, and your receiver at the other end of the HDMI link, the HDMI sound card on those cards does not change the audio.
    Reply
  • Salfalot - Monday, June 13, 2011 - link

    I think I did not use the right word, as I meant the levels of decibel the fan of the cards produce and not the audio too and through speakers.
    All reviewed cards have a fan on them and since most of the HTPC setups are in the living room it would have been nice to know which of the cards are most silent.
    Reply
  • ganeshts - Monday, June 13, 2011 - link

    Though we considered cards with fans in this review, we made it a point to note that the same configuration (GPU model + DRAM bus width + operating frequencies) can be obtained with passive cooling from other vendors.

    For example, the 6570 has a passively cooled model from HIS with the same config and Zotac has a passively cooled 430 too. Other vendors have also demonstrated passively cooled models in Computex.
    Reply
  • cjs150 - Monday, June 13, 2011 - link

    Firstly, a truly informative article. Very high quality.

    The fact that none of AMD, Intel and Nvidia can lock onto to the correct frame rates is unforgiveable. It is not as though these frame rates have changed over the last 6 months. It should not be necessary to be an advanced HTPC user and delve into custom creation of frame rates.

    I really hope that the representatives of AMD, Intel and NVidia are hanging their heads in shame at such basic errors - sadly I doubt they care.
    Reply
  • Grasso789 - Monday, January 28, 2013 - link

    The mistake is rather with Microsoft. Video playback speed should be adapted to the refresh rate of the grafx card. There is a software called Reclock doing that. Then, for example 23,996 Hz can be run with a monitor refresh rate of n times 24 Hz. (The same with audio, because bit-perfect transmission only works with synchronization.) In the end and for most sources, the RAMDAC needed only (multiples of) 24, 25 and 30 Hz. In any system, one of its parts should be the clock master, while the other parts serve. Reply
  • casteve - Monday, June 13, 2011 - link

    Excellent review, Ganesh! Your HTPC insight/reviews have been missed. Reply

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