How to render at 352*576 while keeping the right proportions on display ?

[ppravier]

Hello,

I don't know how to generate movie in the half resolution (352*576 in PAL) that displays correctly ? In fact, each time I create an AVI file having this resolution, it is displayed twice as high as it should be.
If I play an AVI directly generated by the MArvel at the 352*576 res, it is not like that, the proportions are the same than in 352*288.
I tried to generate my file using all the possibilities (Frame, field-A, field-B) without any changes. I noticed that Frame or Field-B gives the best results (and they are identicals) in terms of image quality, but of course the ridiculous proportions stay the same.
I believe than if I have a source AVI beingin 352*576, I should generate an aVI of the same res, no ? In this case why I cannot obtain a correctly displayed file ???

I use MSP 5.2

Pierre-Philippe Ravier

[Rick6612]

Hi Pierre-Philippe,

I'm not exactly sure what you are trying to do based on your message. I can tell you that when you work with the half resolution settings (352x576 PAL or 352x480 NTSC), the Marvel automatically "translates" between the normal video frame size and the half resolution frame size.

In other words, you can capture a normal video image using the 352x576 capture setting and then play back the resulting .avi file and the video image will apear to have the same proportions as the original input video image.

Does that help any?

Rick

[ppravier]

Hello,

I think that I am not enough clear on my message. My question is : how can I generate an AVI file, being in 352*576, using Media Studio Pro 5.2 ? I don't want that the generated AVI file is twice as tall as it should be (but I obtain always something like that). As you said, the Marvel seems to correct that automatically, on AVI coded by itself (that is : in Matrox MJPEG). But an AVI file being coded in Indeo 5.10 or with any other coded different than Matrox MJPEG will be rendered in a very tall windows.

In other words : I think that an AVI file, with a resolution of 352*576 and a Field-based coding, should be displayed in a 705*576 window by the computer. This behaviour is only true with an AVI file encoded with Matrox MJPEG, not anything else.
How can I create my AVI file with MSP, using the Indeo Codec in 352*576, so that it will be automatically be displayed in a 704*576 window as it should be (and not a ridiculous 352*576 window) ?

[jeff b]

The only use I've found for that particular resolution is to save disk space on something that will be played back out to tape, while still maintaining a fairly high level of horizontal resolution. When it is edited in MSP and either played back off the timeline in preview mode for output on a television or tape, the aspect ratio will be okay on the final tape, etc. It is not, however, a resolution setting that is worth using for final output to a file that will not be output to a TV set or tape, because of the problem you describe.

[Grigory]

Hi,

Mentioned resolution is what most VHS users actually need. Using 704 pixels width for (actually) less than 352 pixels horizontal resolution video is wasting drive space.

To get correct aspect ratio for indeo or similar codec, you have to resize the movie to 384x288, or to any size of 4:3 aspect ratio. Resizing results in frame-based video that has less smooth motion. You have to either discard one field, or combine odd and even lines in one while resizing video.

You cannot resize movie to full size, because most codecs will not play the video.

Grigory

[Rick6612]

Hi Pierre-Philippe,

Now I understand what you are trying to do: you want to capture using 352x576 with the Matrox MJPEG codec, but then you want to convert to a different codec (you mentioned Indeo) and not end up with 352x576 proportions.

As others have already said, you can't really do this very easily. When you play a 352x576 Matrox MJPEG video, the Matrox hardware automatically produces a video image of normal dimensions. However, if you convert to a different codec which does not use the Matrox hardware, then this conversion does not take place.

I think your best bet would be to capture at 352x288 and then convert that to Indeo or whatever other codec you want to use. You could continue to capture at 352x576 and then use Ulead MSP to resize the video to 352x288 (or whatever size you want), but the resizing process would take forever. It is probably better to capture at 352x288 up front and then not have to resize.

Rick

[ppravier]

Hello,

many thanks for your anwsers. I am quite disappointed by what you told me because if I understand well, the truth is that the 352*576 resolution is only useful if I plan to generate an AVI file using the MJPEG codec.
In this case I don't understand what is the utility of the FIELDA/FIELDB/FRAME setting of MSP when we generate an AVI file with it.
I thought that if I choosed Field B or A, the media player will understand that each 352*576 contains two frames of 352*288. But It looks that this media player is totally stupid.

As my goal is to store my movie on cd-rom, using a good codec that compress better than MJPEG (which is excellent for editing purposes, but not for storage), I think that the 352*576 resolution is useless for me (as Rick6612 said before).

[This_Idiot]

I'm going to open up an area of discussion here that I am relying on Grigory finishing off for me

Any of the RR/Marvel products only uses field base for full or half size video, because it is assumed at these resolutions the end product is going to be a print to tape for display on a TV.

There is a basic difference between the way that broadcast TV and PCs "see" video. TVs need field interlacing for optimum results.

If your end result is going to be compressed videos for CD archiving then you are wasting time by trying to maintain maximum field resolution throughout the process only to throw it away later. You would be as well choosing a lower capture resolution which is more in keeping with the end result and forgetting about frames altogether.

I'll see if I can demonstrate this by encoding some of the footage that I took for the G400 review tomorrow

[Rick6612]

Hi Pierre-Philippe,

You got the idea now - 352x576 is only useful when you are using the Matrox MJPEG codec. The purpose of this resolution setting is to allow you to capture at a resolution which is adequate for VHS or Video 8, and which uses about half as much disk space as 704x576.

As for the Field A/Field B/Frame Based settings in MSP, the purpose of these settings is to allow you to create a video file with the appropriate attributes for your intended purposes.

If your intention is to create a video that is to be played back using your Matrox hardware for output to video tape and the resolution is 352x576 or 704x576 (352x480 or 704x480 for NTSC), then you will want to use field order B - unless you have an older Matrox Rainbow Runner Studio, which uses field order A.

If your intention is to create a video which is only intended to be used on a computer, probably using a codec other than the Matrox MJPEG codec, then you will want to use Frame Based.

The Media Player is not "stupid" and there is nothing for you to be disappointed about. This is just the way it works. It may seem strange at first, but as you get more experience with it, you will come to understand why things are the way they are.

Rick

[Grigory]

Hi all,

I would like to emphasize another side of PC video here: Aspect Ratio.

RR hardware, as well as many other hardware coders/decoders, is able to keep correct aspect ratio on output screen, 4:3 for TV.
Again, these devices can capture and play video with incorrect proportions between the numbers of pixels along line and number of rows.

For PAL, with 576 active lines, correct aspect ratio by numbers of pixels is 768x576.
Most hardware codecs use different numbers of pixels in digital video: 704, or 352, or 720 for the same 576 lines.

Playing this video on TV, the codecs are able to make each pixel rectangular, thus its width on screen is more than a height. This helps to make a circle shot by camcorder to remain circle on TV screen. This feature is wired into the codec: it simply knows the proportions of a "viewing window" and always fits the frame into this window.


When you convert movie to PC-based codec such as indeo, the only information it has is the number of pixels. Most of PC-based codecs can only display (by default) one pixel of movie frame in one screen pixel. So, the proportions of a movie on screen will depend on the proportions between screen width and height.
Most screen resolutions follow square pixel aspect ratio: 640:480, 800:600, 1024:768, 1152:864, 1600:1200. At this modes, every square of 100x100 pixels is displayed as square, because physical screen dimensions follow the same 4:3 aspect. The pixels have rectangular shape.

The exception is 1280x1024 mode. The correct aspect ratio for this screen width is kept for 960 lines, but not for 1024 lines. So, in 1280x1024 mode, the image height has less centimeters on screen, although the same number of lines. This aspect ratio fits the DV standard proportions. So, a circle shot by DV device is displayed as a circle on PC screen.

Returning back to 352x576 frames, the suitable screen resolution should be exactly 352x576 or 704x1152. Both are not available for video cards.
There are several solutions:
1. Resize a movie frame to screen aspect ratio by number of pixels. For typical screen modes, this gives 384x288, 320x240, 768x576, and others "standard" sozes with 4:3 proportion.
NOTE: 352x288 dimension is incorrect for PC playback, because the image width will be less than desired in centimeters on monitor screen!

2. Play movie as is, but use specialized player that has ability to display frame in a window with correct proportions. Example is old good mplayer.exe, which is still able to play movie in a window of ANY size. you can find this file in your windows directory. You have to resize window manually, with no indicatio of its size anywhere.
It cannot play files longer than 1 GB : the playback stops at 1 GB limit.

Some shareware applications can force windows media player (active movie, windows media, other cabbalistic names from MS for the same thing) to play movie with specified by user frame size on screen.

Be aware that when the image is resized on screen during playback, this may produce some defects, or take more CPU power, depending on the application and video card capabilities. Even simple zoom to 200% works well only in those modes of videocard operation, which support hardware scaling and filtering.
Otherwize you see jaggy diagonal lines, because all image elements are composed from groups of 2x2 pixels. An example is pure RGB uncompressed video.
For Matrox MJPEG, and for DVD players, the player is able to feed video card with suitable type of decompressed video data, like YUY2 (a special "substitution" of truecolor RGB), and force a card to do hardware scaling and filtering. The frame image is resized with interpolation, thus forming smooth frame pictures with good looking edges and diagonal lines. This image is somewhat similar to what you see on TV screen, although the nature of smoothness is different.

You can try to find suitable player on http://www.winfiles.com

You can easily re-calculate all above digits for NTSC.


Grigory

[SteveR]

Does anyone know how to obtain correct 4:3 aspect ratio (eg 320x240) when using mjpeg capture option? I eventually want to end up with an mpeg with correct proportions for viewing on PC.

When using rgb I can select 320x240 and obtain an avi which plays with the correct aspect ratio and converts to an mpeg with correct aspect ratio for viewing on PC.

If I choose mjpeg to reduce file size of intial capture then I only have options with incorrect aspect ratio like 352x288 (PC-VCR or av_io). The avi displays with incorrect aspect ratio and of course so does the eventual mpeg.

The only options seem to be to re-scale 352x288 avi to 320x240 or put up with large avi file sizes.

[Grigory]

Hi,

For MJPEG files played on PC screen with PC VCR application, there is an option called "correct square pixel". It works only for Matrox MJPEG files.

You cannot make Matrox MJPEG avi with 320x240 frame dimensions.
One possible solution for this format is to make movie of 352x288 (240 in NTSC), and put in it resized original frames with correct aspect ratio of 352x264 for PAL or 320x240 for NTSC, leaving the black borders around the movie picture - at top and bottom for PAL, and on left and right for NTSC.

Grigory