Encoder FAQ
 | Profiles |
To ensure maximum compatibility with existing MPEG hardware, the HDX4 codec is equipped with several profiles for different target platforms. For example mobile phones don't support B-frames and offer only a limited resolution. The "mobile" profile will thus optimize the encoding process for this particular hardware.
| MPEG quantization |
If you enable this option the HDX4 encoder will use a matrix-based quantization procedure instead of the default uniform method. Many users say that when using the MPEG quantization option the picture is sharper but it may also appear grainier and richer in contrast. However, if MPEG quantization is disabled the picture may appear washed-out but also cleaner. Eventually, the choice is a matter of personal preference.
| Quarterpel |
If you enable Quarterpel, HDX4 will perform its internal movement approximation with quarter pixel precision instead of half pixel precision. Quarterpel allows for a higher compression and leads to a sharper and more detailed video picture.
The drawback is that this mode is very time-consuming. If you enable Quarterpel, encoding and decoding will suffer from a speed loss of 20% and 50% respectively. In addition to that, some viewers don't like the effect that it has on the displayed picture. It is recommended to enable this option if the currently selected profile allows it and there are no personal objections.
| Is input interlaced |
In contrast to the cinema, TV equipment or video cameras use the interlaced format which means that they store twice as many frames per second but only half a frame at a time. On a computer this display mode has been discarded long time ago as it leads to flickering. That is why the half frames have to be converted to full frames for displaying. HDX4 can take care of this process for you and create progressive video from your interlaced source material. Please select "De-interlace" to remove interlace artifacts from the material. However, if you are planning on displaying the target material mainly on TV equipment you can also keep the half-frames and encode your video as interlaced. In this case please select "Encode as interlaced".
Please note that you always have to check "Is input interlaced" if you use half-frame based material in order to avoid distortions. It is also important to set the correct field order. The correct setting depends on your source material. For material filmed with a digital video camera (DV or miniDV) please use "Lower field first".
| B-Frames |
You can enable bi-directional encoding here if it is supported by the currently selected profile.
| Custom FourCC identifier |
Video players identify the codec used to playback a video using a special identifier embedded in the video file. If you use older hardware or software that does not recognize HDX4 encoded material as MPEG4 you can change this setting.
| Bit rate control |
You can select between "single-pass" and "two-pass" mode. For better understanding, here is a small excursion: By giving the encoder a certain bitrate it receives some kind of a budget. For each second only a given maximum of data may be produced. Depending on the kind and complexity of the material this restriction may lead to more or less visible compression artefacts. If there is a lot of movement in a scene the bitrate needed to encode the material will be higher, whereas in a rather static sequence less space is needed. Videos with a lot of picture noise, fast cuts, fades and a lot of movement are particularly difficult to encode.
When using "single-pass" encoding the encoder must always cope with the given bitrate over a short span of time. However, when using "two-pass" the encoding procedure consists of two or more steps. In the first step the video is only analyzed in order to find out which more or less complex scenes it contains. Based on the collected information the second pass can then distribute the given bitrate over the whole length of the movie. Complex scenes get a higher bitrate assigned and rather static scenes are encoded with a lower bitrate. This leads to a much more constant and higher quality with a bitrate that is constant regarding the complete clip but varies over the duration of the film depending on the material. If you have enough time at hand you should always prefer the "two-pass" mode, as it provides a definitely superior quality.
| Target bitrate |
You can set your desired video bit rate using a slider or directly by entering a value. Please note that you cannot set a bit rate for the rate mode "two-pass - First run" since in this mode the video is only analyzed and no actual encoding is done.
You can change the entering mode for the destination mode by clicking the button "Target bit rate" if the currently selected profile allows it. Apart from setting a fixed bit rate you can also set a quality value in percent or a quantization factor. 0% stands for worst quality and highest compression, 100% stands for best quality and least compression. The lower you set the quantization factor, the better the quality becomes.
Please note that you cannot set a bit rate in quantization or quality mode. Instead your setting will indirectly influence the target bit rate. Since not all target devices support quantization you should ensure that the result is compatible with your hardware.
| Pixel aspect ratio |
Computer displays use square pixels, i.e. when playing videos with an aspect ratio of 1.33:1 (4:3, for instance 640x480 pixels) these videos are really played back in this aspect ratio. For such videos you can deactivate the checkbox "Pixel aspect ratio". The default ratio of 1:1 will then be set.
In contrast to this, TV screens use a pixel aspect ratio of 1.067:1. For instance DVD videos usually have a picture resolution of 720x576 which equals a pixel aspect ratio of 1.25:1. Since TV screens also have an aspect ratio of 1.33:1 these videos have to be aspect-corrected by 1.067:1 in order to be played back without distortion. Please use "DVD 4:3 (PAL)" or "DVD 4:3 (NTSC)" for such material. In Europe the PAL system is used.
If you use anamorphic material from DVDs you have to select "DVD 16:9". 16:9 material is stretched to full screen size in order to provide a 33 percent higher line resolution on widescreen TVs. However, since not all devices support anamorphic MPEG4 material you should check your manuals to find out if your hardware player supports it.
| Quality |
The quality selection has the highest impact on the time consumption during encoding. The higher you set the quality the more time encoding will take but the better the result will be. When capturing video in realtime please use the "realtime" mode which will adjust the quality to the speed of your computer system and automatically enable or disable certain features to avoid frame-drops.
| Psychovisual enhancements |
"Psychovisual enhancements" is an umbrella term for methods to reduce complexity within a video stream in a way that the human brain is least likely to notice. You should experiment with this setting to find out if you are disturbed by the effect it has.
| Max key frame interval |
An encoded HDX4 video does no longer consist entirely of complete frames, it rather contains a majority of frames that only describe differences between a picture and its predecessor. During playback the full frames are reconstructed. Since this leads to much lower space requirements you should not set the maximum keyframe interval too low. However, if you experience delays when skipping within a video file you can lower this setting.
| Optimize for film source |
Cinematic productions are filmed on celluloid and have a natural graininess. Depending on the film material experts can for instance still tell the difference between Super-8 and 35 mm material even on a DVD. Video without grain and with many single-colored areas can be encoded more easily but it looks less natural. The user should try encoding with and without simulated grain in order to find out which he likes best.
