View Profile
View Forum Posts
I was always taught that the best way to take 720 x 480 AVI video to a web format was to crop off the 16 pixels of overscan, then resize the video to 640 x 480 for web formats like MP4 and WMV. I recently began working for a company with other editors and one of them resizes the AVI video to 720 x 540 pixels for the web, thus stretching out the vertical resolution to make a 4:3 match with the horizontal. It seems to me that this is not a good way to proceed because of blurring caused by stretching out the pixels, but having others confirm that this is not a good approach would be appreciated before I bring it up to the owner of the company. I know most newer devices do not have this limitation, but just the 640 x 480 limits on some mobile devices makes it seem like a bad enough idea to me.
+ Reply to Thread
Results 1 to 24 of 24
-
-
A Member since June, 2004
- Feb 2013
- Westernmost point of Europe
I think your approach is correct since it mantains the number of scan lines and adjusts the width sampling. As for the cropping of the 16 pixels, although it follows the ITU recommendations, I think it is not always the best way to go, since video sources somrtimes don't comply to said recommendations and make use of the entire 720 pixels. In such cases it woulb better to resize 720x480 to 640x480 without cropping.
"The greatest trick the Devil ever pulled was convincing the world he didn't exist." -
Is it interlaced 720x480 like from DV ani or mpeg2 originals?
In that case, another aspects are involved - aspect ratio, resizing of interlaced video -
That's a good way to stir up animosity at work, disrupt morale, and maybe get you fired eventually. Don't assume that the company really cares so much about SD broadcast quality, they don't.Originally Posted by devkel
-
_Al_,
There are 720 x 480 DV AVIs, standard (.9091) pixel size, bottom field first interlaced files as well as 720 x 480 MPEG 2 files, also standard size with bottom field first deinterlaced. As there are only 480 vertical pixels, I can not see any way that stretching them to 540 would not cause an unnecessary loss in picture quality. And though it is not as big a deal now, it would also eliminate playback on devices like iPods as well. -
On the other hand resizing them to 640x480 causes a loss of horizontal resolution. So either way you lose.Originally Posted by devkel
-
jagobo,
As we are taking video with anamorphic pixels and displaying them on devices with square pixels, keeping the horizontal pixels at 720 is going to stretch out the horizontal. 720 - 16 overscan pixels *.9091 is going to be 640 pixels for square pixel devices. Whatever might be lost in that conversion seems better than making everyone in the videos gain 25 pounds by being stretched horizontally. -
Only if you play it in a 640x480 window. If you're going to view it full screen it will be played at whatever your screen resolution is (letterboxed or pillarboxed if the DAR doesn't match the screen). So resizing to square pixels will result the video being resized twice before you see it. Most players support anamorphic playback now. I haven't used square pixel encoding for non-square pixel sources in years. Yes, resizing for online playback is different.Originally Posted by devkel
-
But does your videos have black bars at sides? That crop 8pixels from left and 8 from right makes aspect ratio to not be real then. Is it not visible? Never tried it, cannot say what looks better, DV avi has all 720 horizontal pixel used up so I used to keep them. So no cropping, just resizing to 640x480.
-
DV uses ITU aspect ratios so the DAR is in a 704x480 or 704x576 portion of the frame. DVD uses MPEG aspect ratios so the full 720x480 or 720x576 frame represents the DAR. Of course, most DVDs made from analog tape ignore the difference between ITU and MPEG aspect ratios and they just treat the ITU cap as MPEG.
In either case, you can use the SAR to specify the correct aspect ratio when using anamorphic encoding with MPEG 4 part 2 (Divx/Xvid) or part 10 (h.264/AVC). -
Last edited by _Al_; 26th Oct 2014 at 20:18.
-
There's nothing to say media players are resizing correctly. According to jagabo (and I'm happy to take his word for it) DV always uses an ITU aspect ratio, so for 4:3, rather than it being resized to exactly 1.333333, the aspect ratio is around 1.3675. In other words 704x480 gives you an exact 4:3 aspect ratio (the extra 8 pixels each side aren't included), which means the whole 720x480 frame should be resized slightly wider. Software players just see a 4:3 aspect ratio, so that's what they do.Originally Posted by _Al_
That also applies to pretty much all 4:3 DVDs. You can easily correct it (or get it closer to correct) using MPC-HC by tapping the 6 key on the numeric keypad. I don't have any 4:3 DV AVIs to check, but software players all resize 4:3 DVD video to exactly 4:3 (as far as I know), and while it's not always the case, in my opinion 99% of the time it'd be wrong. If DV AVIs are supposed to be resized the same way (704x480 = 4:3), then they're probably being displayed incorrectly too.
As the 8 pixels of crud each side isn't always crud.... sometimes it's picture.... depending on the amount of cropping required I sometimes resize 4:3 DVDs to 656x480 when re-encoding as it's closer to the correct aspect ratio when the entire 720x480 frame is resized.
My opinion regarding the OP's question......
In my experience resizing a 720x480 video to 720x540 rather than 640x480 generally goes into the pointless category. I've compared the two lots of times running full screen on my TV (re-encoding DVDs) and there's virtually no difference in respect to picture detail, although I assume the sharpness of the resizer could also be a factor. Sometimes rather than blur it may do the opposite. I know there's technical reasons for leaving the vertical resolution untouched but mostly it's going to be resized on playback anyway, so while generally I'd put 720x540 in the "why bother" category, I've resized that way on occasion when I thought the result was better (seemed to retain more picture detail). -
What about just cropping the overscan pixels (provided they are bad) and no resizing?Originally Posted by devkel
-
Probably because it's for the internet and it'll keep the bad aspect ratio unless resized.Originally Posted by newpball
What about just cropping the overscan pixels (provided they are bad) and no resizing?
-
Sorry but what is bad about it?Originally Posted by manono
Probably because it's for the internet and it'll keep the bad aspect ratio unless resized.Originally Posted by newpball
What about just cropping the overscan pixels (provided they are bad) and no resizing?
-
What's bad about uploading (for YouTube, for example) something that's 720 or 704x480? Because it's not in the correct aspect ratio and people will become slightly fat. As maybe you know (or don't know) DVDs aren't displayed at 720x480, but get resized for display depending on whether the DAR is 4:3 or 16:9. If all this is Greek to you, then read this:Originally Posted by newpball
Sorry but what is bad about it?
http://www.doom9.org/aspectratios.htm
Internet players (such as YouTube's) won't do the resize. So you have to do it before uploading (or do it with a tag after the upload). That means resizing to some 1.33:1 ratio such as 640x480.
If you like the fat people you'll see with a 4:3 720x480 video on YouTube (it's full of them), then I can't help you. -
Nope, it is no problem cropping a 4:3 video, as long as you encode them in the proper format they do not get stretched at all. Frankly I think it is kind of ludicrous to suggest you cannot upload a video into a 16:9 box without stretching or squeezing unless it is pure 4:3 or 16:9, it is simply not true.Originally Posted by manono
What's bad about uploading (for YouTube, for example) something that's 720 or 704x480? Because it's not in the correct aspect ratio and people will become slightly fat.Originally Posted by newpball
Sorry but what is bad about it?
You can easily place a cropped 4:3 video in an 16:9 box, you will obviously get black bars left and right but you get that anyways so a few extra pixels is not going to make any difference and for that you do not need to resample the video, in fact doing that could be detrimental to the quality.Originally Posted by manono
There are many more aspect ratios all the way from 1.19:1 to extreme widescreen all of those can be all conveniently fit in a 16:9 box and it is not required to exactly fit either the horizontal or vertical bounds of youtube, it may be useful but not always.Last edited by newpball; 28th Oct 2014 at 19:55.
-
That makes no sense at all. I said if you upload a 720x480 video, in whatever format you like, YouTube will display it at 720x480 and in the wrong aspect ratio (unless you add the 4:3 tag). Do you disagree?Originally Posted by newpball
Yeah, sure, but 720x480 isn't 4:3, it's 3:2. And it'll be shown in the wrong aspect ratio. And resizing is necessary. The small degradation caused by the resize alone is nothing compared to the damage YouTube does to all the videos uploaded when they're reencoded at low bitrates. The thread is about how to resize for Internet streaming. Of course you can set a SAR and not resize at all for viewing on many home and computer media players.You can easily place a cropped 4:3 video in an 16:9 box, you will obviously get black bars left and right but you get that anyways so a few extra pixels is not going to make any difference and for that you do not need to resample the video, in fact doing that could be detrimental to the quality. -
Manono, NTSC does not use square pixels.
Bottom line is that you can easily crop a little from the left and the right of the video source then encode it standard NTSC 4:3 format and Youtube will render the video just fine. The black bars left and right will be a little bit bigger because of the crop but nothing is squeezed or stretched. No need to resample the video source!
Resizing a video source sometimes makes sense, for instance if you are merging clips with different resolutions, but most of the time it is best to just leave it alone.
-
This isn't about PAL or NTSC but how to upload for streaming so it gets displayed in the right aspect ratio. Everyone that's posted in this thread understands that but you.Originally Posted by newpball
Answer the question. A simple 4:3 DAR 720x480 video, like the OP had when he asked the best way to resize it for Internet streaming.Originally Posted by manono
-
This is going nowhere, if you think you must resample a video if you crop a few pixels left and right to prevent a video from being stretched or squeezed then so be it, it seems I won't be the person who will convince you you do not have to.
By the way I do this all the time, cut of parts of an SD video, encode it, and guess what it comes out just fine, the black bars will just be a bit larger!
-
You have to resize when uploading to a streaming site. Whether you cut a few pixels from the sides or not has nothing to do with it.Originally Posted by newpball
And then you upload it to YouTube, right? And you couldn't even answer the simple question I posed twice?By the way I do this all the time, cut of parts of an SD video, encode it, and guess what it comes out just fine
I get it now. You're a troll having fun trying to make people mad. And to think I actually took you seriously. Silly me. Either that or you're incredibly ignorant. Have fun. -
Created two standard NTSC videos in MP4 with a resolution of 720x480. One with a full frame another one with a cropped frame. Uploaded both to Youtube. They show just fine, not squeezed or stretched, and all that without me requiring to resample the video.Originally Posted by manono
You have to resize when uploading to a streaming site. Whether you cut a few pixels from the sides or not has nothing to do with it.Originally Posted by newpball
And then you upload it to YouTube, right? And you couldn't even answer the simple question I posed twice?By the way I do this all the time, cut of parts of an SD video, encode it, and guess what it comes out just fine
I get it now. You're a troll having fun trying to make people mad. And to think I actually took you seriously. Silly me. Either that or you're incredibly ignorant. Have fun.
https://www.youtube.com/watch?v=im5fObkhtLY
https://www.youtube.com/watch?v=7lucY3rwwA8
Attached is the file info for both videos right before they are uploaded, as you can see they are both 720x480:
Last edited by newpball; 29th Oct 2014 at 09:57.
-
Well, you were right and I was wrong, and I apologize for doubting you before doing some tests of my own. YouTube has changed the practice of assuming everything uploaded is 1:1, and now takes the SAR or DAR into account.
I uploaded a 720x480 MP4 with an 8:9 SAR and got a 640x480 video. I uploaded a 4:3 VOB and also got a 640x480 video. It was uploaded VOBs and MPGs I had studied before that always played with the wrong aspect ratio. As I mentioned, they even developed tags to correct the problem, it was so bad:
https://support.google.com/youtube/answer/146402?hl=en
I have no idea when the change was made. I do, however, have some comments:
1. You were unspeakably obtuse in not answering my simple question. Had you said 'Yes' when I asked if 720x480 would play at the right aspect ratio, I'd have immediately gone and checked for myself.
2. I got 640x480 in my tests and have no idea how you got 652x480. ITU resizing, maybe, using a different SAR value?
3. YouTube resizes when reencoding and not just when playing it. That is, your videos when downloaded were 652x480 and not 720x480. You mentioned being spared degradation of the video by uploading 720x480. As you put it, "you do not need to resample the video, in fact doing that could be detrimental to the quality." But it gets 'resampled' anyway and I'd rather I do it myself than have YouTube do it.
But there's no getting around it - you can upload a 720x480 video with the right SAR/DAR and get it to play at the correct aspect ratio on YouTube. Not that I'll ever do that myself. Thank you for the lesson.
Quote