352x576 re-encoding problem

[lascetic]

I have a standalone dvd recorder that records vhs into 4:3 pal 352x576 vobs. I am trying to re-encode the vob into mkv but the result is a narrow strip of video, like a vertical rectangular. I am using MeGUI for the first time, so I was wondering if there is a way to pre-define the 4:3 aspect ratio. Is it something I can do with MeGUI or should I add something on the script?

[jagabo]

Aspect ratio signaling:
http://mewiki.project357.com/wiki/MeGUI/Aspect_Ratio_Signalling_in_AviSynth_Scripts

[lascetic]

Hi and thank you for the information. As I said, I am new to this and I don't understand much of the jargon. So, if I add
global MeGUI_darx = 4
global MeGUI_dary = 3

in my script, will that do the trick? Do I have to add anything to MeGUI or add any resizing lines to the script? And finally could anyone explain to me what do the following lines do and if I need them?

global MeGUI_darx = my_avs_func_x()
global MeGUI_dary = my_avs_func_y()

[jagabo]

Just paste:

global MeGUI_darx = 4 
global MeGUI_dary = 3

into your script. It worked when I converted a 352x576 file to MKV.

[lascetic]

Just paste:

global MeGUI_darx = 4 
global MeGUI_dary = 3

into your script. It worked when I converted a 352x576 file to MKV.

I just tried it but it didn't work. Can I put it anywhere within the script?

[jagabo]

I'd put it at the start of the script, just to be sure. Did the preview window show 4:3 DAR at the bottom?



Note that some players may not respect the aspect ratio flagged in the header.

[lascetic]

Yes it does. I tried with vlc and pot player






MediaInfo gives 0.651 aspect ratio for the MKV whereas it gives 4:3 for the initial vob.
I also tried to paste it in various positions in the script.

[jagabo]

I wonder if some of the presets override the AR flag? I used "x264" Unrestricted 1pass Const. Quality Fast" when I tested it. Both MKV and MP4 output had 352x576 frame sizes with 4:3 DAR set in the header. MediaInfo showed the same. VLC and PotPlayer play both of them with the correct 4:3 DAR.

[lascetic]

Here is my script and the MeGUI settings:

[jagabo]

That's essentially the same as the script that I used. Try adding Info=3 to Mpeg2Source(), after CPU=0.

[lascetic]

That's essentially the same as the script that I used. Try adding Info=3 to Mpeg2Source(), after CPU=0.

It didn't work

I even tried to do everything from the beginning, but still.....

[poisondeathray]

post your megui log file

maybe it's a playback issue ? How are you playing the encoded file ? What software ? Try something different like VLC, MPCHC, Potplayer , does it make a difference ?

[jagabo]

I just noticed "--sar 16:15" in the x264 command line. That's not right. It should be 24:11.

[poisondeathray]

jagabo is right

Go into the advanced settings and look at the command line box and see if any values are entered in (some presets have values entered)

If not, just enter --sar 24:11 in the box , but erase the Megar_dar_x , y stuff from the script first

[lascetic]

I just noticed "--sar 16:15" in the x264 command line. That's not right. It should be 24:11.

When I do the sar test for Pal full screen 4:3, I only can choose between ITU 12:11 and Non-ITU 16:15.
12:11 seems a bit stretched (to my eye)

@poisondeathray
I tried all 3 players you mention with the same result. The thing is that the converted file in MediaInfo shows 0.651 aspect ratio. Log file attached.

[jagabo]

When I do the sar test

I don't know what you mean by "sar test".

for Pal full screen 4:3, I only can choose between ITU 12:11 and Non-ITU 16:15.
12:11 seems a bit stretched (to my eye)

352 * 24 / 11 = 768
768 / 576 = 4/3

[lascetic]

I don't know what you mean by "sar test".

Well, the tutorial from which I am learning loads this script to avisynth and by setting the values for pal/ntsc and wide/full screen you can compare the same frame as ITU or non-ITU and determine the SAR. Maybe it doesn't work for all videos or the tutorial was not detailed and I missed something.

Anyway 24:11 seems to have done the trick
Could you please elaborate a bit more over (or refer me to) how does one determine the SAR value? How does one know if it is ITU or non-ITU?

Oh and another thing. Shouldn't it be 720 rather than 768 since the original source is vhs?

I really appreciate your help and patience.

[manono]

Shouldn't it be 720 rather than 768 since the original source is vhs?

No, and the original source hasn't much to do with it. You want it to play in a 4/3 or 1.33:1 ratio, one such as 768x576. If you used a SAR that output 720x576 that ratio would be 5/4 or 1.25:1 and people would appear slightly too thin and too tall. Round things would be slightly oval-shaped. A 720x576 DVD, for example, gets resized during playback to either a 4:3 or 16:9 ratio, depending on the DAR set while encoding. VHS tapes, though, are always 4:3. And they use ITU resizing.

I think that's right. jagabo can confirm (or contradict).

[jagabo]

Could you please elaborate a bit more over (or refer me to) how does one determine the SAR value?

DAR = FAR * SAR

DAR = display aspect ratio (shape of the final displayed picture)
FAR = frame aspect ratio (relative frame dimensions)
SAR = storage aspect ratio (aspect ratio of individual pixels)

4:3 = 704:576 * 12:11
4/3 = 704/576 * 12/11
4/3 = 704 * 12 / (576 * 11)
1.33 = 1.33

How does one know if it is ITU or non-ITU?

The ITU spec for digitizing analog video indicates that a ~702x576 pixel frame contains the 4:3 (or 16:9) image. That's generally just rounded to 704x576 to keep mod 16 frame dimensions. (It's actually even more complicated than this but I'll ignore those complications.)

The DVD spec refers to the MPEG 2 spec for aspect ratios. The MPEG 2 spec does not specify the sample aspect ratio, only the display aspect ratio -- so, the final shape of the picture can be either 4:3 or 16:9 (as far as DVD is concerned). It has no direct method of specifying the sample aspect ratio.

This leads to a problem: Most PAL DVDs use a 720x576 frame size. But an ITU spec capture uses a 704x576 frame size, usually padded with another 8 pixels at the left and right edges to fill out a 720x576 frame. Since the 4:3 image of such a capture is stored in the inner 702x576 pixels the full 720 pixel wide frame is slightly wider than 4:3. But the MPEG 2 spec has no way to account for that (actually it does but it's never used). The issue is mostly ignored by producers of DVDs and by DVD players. ITU captures are just mastered to DVD as is. In my experience, players use the ITU spec at their analog outputs (s-video, composite) but the MPEG 2 spec at the HDMI output.

Generally, nobody notices the ~2 percent difference between the two specs. But if you're a stickler for accuracy there are a few methods for determining whether the pixels are ITU or MPEG 2. If you have a 352x576 or 704x576 frame then the ITU and DVD specs are essentially the same. If you have a 720x576 frame with obvious ~8 pixel borders left and right the video was probably digitized from analog tape following the ITU spec then simply mastered to DVD. If there are no borders the DVD probably follows the MPEG 2 spec. To be sure you have to find an object of known aspect ratio and measure it on-screen.

[lascetic]

That's really useful information. I appreciate your help. I'm gonna take advantage and ask a couple of more questions. First. what would be the difference if instead of adding the lines
global MeGUI_darx = 4
global MeGUI_dary = 3
I have added a resize command in the script, say for example Spline36Resize(768,576)? Would this have the same results?

Secondly, is there a way to remove (at conversion) the black bars that appear on the sides of the film when played in full screen, without a distorted outcome?

[jagabo]

That's really useful information. I appreciate your help. I'm gonna take advantage and ask a couple of more questions. First. what would be the difference if instead of adding the lines
global MeGUI_darx = 4
global MeGUI_dary = 3
I have added a resize command in the script, say for example Spline36Resize(768,576)? Would this have the same results?

I don't really use MeGUI so I'm not familiar with its peculiarities. But if it encodes the 768x576 frame as square pixel (1:1 SAR) then you'll be ok. But some programs try to be "helpful" and make adjustments for you -- screwing up the picture in this case. Try it and find out.

Secondly, is there a way to remove (at conversion) the black bars that appear on the sides of the film when played in full screen, without a distorted outcome?


[Attachment 21263 - Click to enlarge]

No, not without distorting or cropping the frame.

[lascetic]

No, not without distoring or cropping the frame.

How many pixels per side should be cropped to remove the bars from a 352x576 video and what would be the result dimension-wise and image-wise? Will it be stretched? Will there be image lost? Sorry for bombarding you with all these questions, but I guess I opened the pandora's box.

[jagabo]

You want to crop from the top and bottom to make 16:9 out of 4:3 DAR material -- a total of 144 lines, leaving 352x432 (24:11 SAR) or 768x432 (1:1 SAR).

[lascetic]

You want to crop from the top and bottom to make 16:9 out of 4:3 DAR material -- a total of 144 lines, leaving 352x432 (24:11 SAR) or 768x432 (1:1 SAR).

Brilliant! I can't thank you enough for your patience. I learned many things, thanks to you.