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Old 5 Jan 2003, 07:57 PM   #1
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Question-2 How to deal with the quality of the source file to encode for VCD (PSX:str)...?

I've been testing some encoding and I came up with several questions. I hope someone would help me to answer them:

Goal:

I want to transfer some PSX .str movie files to make a compilation VCD. I have the PSX Multi Converter software to convert them to divx5 avi files or other avi formats (I don't use the .str TMPEnc plugin since it doesn't search for all the .str a PSX CD could have).


Spec:

.str files are usualy 340*224, 15fps, 3322ko/s wich are converted by PSX to 640*448, 30fps (interlaced) in NTSC regions.

I use the divx502 codec and TMPGEnc software to make VCD's and Virtual Dub.

PIII 800MHZ FSB 133MHZ, 128MB RAM, Radeon 7500 64MB VRAM, SBPCI 128.

Questions:

1- Regarding the divx5 encoder, I was wondering which bitrate and mode to use for encoding. I know that the .str files have a bitrate of 3322 ko/s (uncompressed frames with 15fps(30fps internal) and 320*224) and I know I want to make a VCD wich is 1150 ko/s, 29.97fps, 352*240. So is there a point to encode with a bitrate more than 1150 ko/s with divx 5 ?

2- I've done some testing and many questions came up. I tried first to save the .srt file on an uncompressed avi file (3322 ko/s...big file so quality source expected) and then convert it with TMPGEnc (VCD, NTSC) in mpg-1 format. Then I tried the same thing but with the .str file compressed with divx5 (quality based = 100). First I was wondering why the divx5 file was only about 6Mb large (about 600ko/s for a 20s test file while the uncompressed file is about 40MB) even if I used a quality base = 100 (I tested also 2-pass with 10000ko/s and it was the same result) ? . Then I was wondering why the quality of the final mpg-1 file is better when using the divx compressed file instead of the uncompressed file? Does the divx5 codec optimize something in the file ? (Note that PSX movie are not top noth DVD quality)

So basicaly, is it better to have a source file greater than 1150ko/s when making a VCD ?

And if it is the case(size of the source doesn't matter since I will delete it after making the VCD) should I always use 1 pass quality encoding = 100 for PSX movie ripping?

What would be the quality wise settings (size doesn't matter here) ?

Does the divx5 codec settings "Global Motion Compensation" "quarterpixel" and "B-frames" help only to increase quality or is it for the quality/size ratio ?

3- I tried also an option in PSX Multi Converter to extract the .str file with double the resolution (640*448 instead of 320*224) and made a divx5 file. I realized that the final mpg-1 looks far better (clearer edges and overall smoothness) than extracting in 340*224. I was wondering if I would obtain the same result by first extracting the .str file on a divx5 file of 320*224 and then resizing it with Virtual Dub (precise bilinear)? Does resizing always gives these results or is it that the real resolution of .str files are 640*448?

For future references:

4- I would like to know what will happen if for exemple I have a source file of 2000ko/s and I compress it with divx5 with a setting of 4000ko/s ? (out of sync? )

5- Is it possible that when encoding a so-so quality source file with a really high bitrate it introduces some artefacts (Even if the source has a higher bitrate tham the encoding)?

6- In making a VCD, does it bother to have a really great source or is it preferable to use a source that is closer the the spec of a VCD file (mpg-1) ?


Thank You in advance

ripley_B

Last edited by ripley_B; 5 Jan 2003 at 08:04 PM
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Old 6 Jan 2003, 05:58 AM   #2
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The short answer is - As long as you've got sufficient hard drive space to temporarily store the uncompressed original resolution video, that's the way to go. Simply stated, the better the input quality, the better the output (VCD) quality.

Since I see you're in the NTSC world, I'd suggest that you do the conversion at 23.976Fps, rather than 29.97 (You may or may not have to select "Inverse Telecine" from within TMPGEnc's filters and tools listed under the "Advanced" tab) - results in smoother playback.
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