Motion search and VCD's ??

[TheLostTimberwolf]

If making a standard 1150 kb/s VCD with tmpgenc does the motion search make a difference?

I understand that the search locates scene changes and action/motion or lack of it, in the video stream so the program knows how to allocate the bitrate. But if its a constant bitrate would it need to know?

also, if converting from a DivX avi file to vcd wouldn there be any need for a de-interlacer? I have read that all DivX movies are progressive is that true?

thanks... 8)

[adam]

First off, motion searching is something that is always done when encoding mpg, even in CBR mode. TMPGenc just allows you to set the priority of this feature, most encoders presumably just use what their programmers determine to be the best tradeoff between speed and quality.

To answer your question, yes absolutely motion searching is still important even when encoding in CBR and even with such a low bitrate. Just think about what bitrate refers to; its the bits per SECOND that are applied to your film. Yes with VCD you have the same amount of bits per second but within each second you have anywhere from ~24 to ~30 frames. That 1150kbits still has to be distributed to each of these frames according to their complexity and this is where motion searching comes into play. The better the encoder can determine the complexity of each frame, the better it can distribute the bits per frame, even though the same amount of bits is used for every ~24 to ~30 frame interval (1 second).

Essentially, even CBR is still VBR because each frame is given a different amount of bits. The difference is that when encoding in VBR your total number of bits must average out to a specified number throughout the entire length of the film, whereas in CBR your bits must average out to a specified average every second.

To answer your second question, some mpeg4 codecs support interlacing but most don't. Even for the one(s) that do, there would not be a reason to encode interlaced because these formats are intended for playback on pc monitors which are progressive. So essentially, yes all divx are progressive and there is no reason to deinterlace.

[puertorican138]

Motion search precision adjusts how much the encoder searches for motion between different frames. This means it looks at a block in a frame and then looks at the next frame for the same (or similar, depending on other settings) block somewhere else in the picture. If a similarity is found, information on the direction and how much the mpeg block moved between the 2 frames is put into the mpeg stream, so that the block is used
in a different place in frame 2. By doing this the same thing isn't encoded twice. This means that less bits are used when things are repeated. then bits can go to other things like encoding the block better in the 1st frame.

Setting the motion search precision to the highest quality (slowest) setting will make the encoder search really hard for repetition between frames. This makes the picture a lot better when things are moving.

If you encode a video with only small amounts of movement, you can sometimes get away with lower settings to save time, but even in low motion pictures, different parts of the image might be the
same, so I always use the highest setting to give the best picture.

Professional DVD authoring hardware uses extremely sophisticated methods to search for motion, and that's what makes them so expensive, but so high quality.

Hope That Helps!!! :P

[TheLostTimberwolf]

@ adam & puertorican138

Thank You both very much for the detailed information, i was wondering about that for quite some time, but i never actually read the fine print, ie 'frames PER Second'.

muchly appreciated thanks again :P

[puertorican138]

@ adam & puertorican138

Thank You both very much for the detailed information, i was wondering about that for quite some time, but i never actually read the fine print, ie 'frames PER Second'.

muchly appreciated thanks again :P

Anytime! :P