Damn, that's really interesting, thanks a lot Steven! I print your
email, and I'll read it while going to work! ;-)
As regards to the dimensions of the video, for the moment the output
will be displayed on a computer, not on a TV. That's why I tried to
resize the video to fit in a computer monitor.
In the next week, I'll have to produce a DVD however.
Well, I print your email! ;-) I assume I'll have to ask you some other
questions... ;-)
Thanks a lot, Steven!!!
Nicolas, Paris.
On Wed, Apr 20, 2005 at 03:35:41PM -0700, Steven M. Schultz wrote:
>
> On Wed, 20 Apr 2005, Nicolas wrote:
>
> > Damn, y4mscaler and mpeg2enc are driving me crazy... =(
>
> Just takes a little practice :)
>
> > Thanks for pointing me to yuvdeinterlace, Steven! I now use:
>
> Welcome.
>
> > nice -19 lav2yuv record_01.avi | y4mshift -n -2 | y4mscaler
> > -I active=744x560+12+8TL -O size=744x560 -S option=sinc:6 |
> > yuvmedianfilter -T 3 | yuvdeinterlace -f | mpeg2enc -f 0 -V 500 -c -D 10
> > -E -10 -q 2 -K tmpgenc -o record_01_cvs.m2v
>
> > However, as you see, I had to use the -f 0 flag for mpeg2enc. If I use
> > the -f 8 flag as I did before, I have that error:
> > **ERROR: [mpeg2enc] Horizontal size is greater than permitted in
>
> Correct - you can't put 744x560 on a DVD. For 625line ("PAL") the
> valid frame sizes for a DVD are: 720x576, 704x576, 352x576 and
> MPEG-1 352x288. No other sizes are valid. And 560 lines is not a
> valid number of lines for PAL.
>
> http://www.dvddemystified.com/dvdfaq.html#3.4
>
> > And then it stops.
>
> As it should ;) If you tell mpeg2enc it's producing output for a DVD
> then it will enforce the DVD limits on the frame size.
>
> > I need:
> > - a good quality
>
> Then don't deinterlace :) Or rather, if the DVD will be played
> on TV sets then leave it interlaced since almost all TV sets are
> interlaced. OH, and as I mention again later on TVs overscan so
> you will not see the edges that you're trying to crop.
>
> So you will degrade the image slightly by upscaling 560 lines to 576.
> Upscaling introduces no new information, it has to fabricate the new
> number of lines by (basically) interpolation. You'll loose some detail,
> the image will be a little blurrier/softer.
>
> > - a cropped video, with no black borders
>
> Be careful to take into account the fact that video pixels aren't
> square. For PAL the pixels have an aspect of 59:54 (they are slightly
> wider than they are tall). MJPEG cards product square pixels - that
> is why you have a 768x576 frame - 768x576 with 59:54 pixels is the
> same as 704x576 using 59:54 pixels!
>
> Refer to: http://www.mir.com/DMG/aspect.html
>
> In particular the first section with the formula:
>
> width DAR
> -------- = -----
> height SAR
>
> DAR (Display Aspect Ratio) is probably the usual 4:3, SAR for PAL is
> 59:54 and height must be 576. Solve for 'width' (and round up to
> the next multiple of 16).
>
> Or you just leave the math to y4mscaler ;) See below.
>
> > there're some very large green blocks on the right border of the
> > picture. Moreover, there're some parts of the image (with a lot of
> > details) which are "blocky"
>
> Probably because you 1) didn't specify a bitrate and the default is
> very low (~1152Kb/s) and 2) -f 0 is generic MPEG-1 (not MPEG-2).
>
> Then too 744 is not a multiple of 16 and encoders really prefer having
> the dimensions be a multiple of 16 (which 720, 704, 352 are - so is
> 576).
>
> > How can I crop my pictures using y4mscaler? I tried, as given by Steven:
> > y4mscaler -O sar=src size=704x480
> >
> > But that does not produced the expected result...
>
> That's because that was only an example. You were expected to put
> in appropriate numbers for your needs (PAL, input framesize, etc) :)
> I use that step as a final crop before going into the encoder.
>
> Something like this will be a LOT closer to what you need (but I have
> not tested it):
>
> y4mscaler -I active=744x560+12+8TL -I sar=1:1 -O sar=59:54 -O size=704x576
>
> But you really don't want to do that...
>
> That will degrade the image because you're cropping the top
> and bottom 8 lines (total of 16) and then scaling up 560 to 576 lines.
>
> But y4mscaler will do The Right Thing to preserve the aspect ratio.
>
> On a TV set (which others may view the DVD on) the top and bottom
> black bars will NOT be seen due to overscan. TVs lose between 5 and 10%
> of the edges.
>
> A better way to handle the noise in the borders is to turn them to
> pure black but leave them present.
>
> Far better to do something like this using the original full 768x576
> frame that you captured, blacken the top 8 and bottom 8 lines BUT
> LEAVE THEM PRESENT - you must have 576 lines for PAL, not 560!
>
> Use the '-b' option of y4mshift to put black on the borders. Something
> like "-b 12,8,754,560". That is what I do for analog captures - it
> blackens the VCR noise/junk in the borders and allows the encoder
> to use fewer bits to encode the border areas.
>
> The end commands would be something like
>
> lav2yuv ... |y4mshift -n 2 -b 12,8,744,560 | \
> y4mscaler -I sar=1:1 -O sar=59:54 -O size=704x576 -S option=sinc:6 |
> ...
>
> What you can NOT do is arbitrarily pick your size and then scale
> the two dimensions to fit the frame both horizontally and vertically.
> You'll mangle the aspect ratio that way (people will be too skinny or
> too fat and circles will not be round). The number of lines is fixed
> at either 576 or 288, the two aspect ratios are fixed (you can not
> change them as desired) at 4:3 and 59:54 (or 16:9 and 118:81).
>
> If you're making DVDs then there are a lot of restrictions that have
> to be observed. For computer only playback the restrictions are fewer,
> you can set your frame sizes as desired - but for DVDs the choices
> are few and specific and govern how you have to crop and scale the
> image data.
>
> Cheers,
> Steven Schultz
>
>
>
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