Question about 480p video

[Videogamer555]

I want to convert a video to 480p from 1080p to save file space on my harddrive (loss of resolution isn't that important). Now it's a 16:9 aspect ratio video. But the problem is that unlike with 4:3 aspect ratio at 480p, which has an exact integer output for (480/3)*4, it's not the same with 16:9. 4:3 at 480p is simply 640x480, but with 16:9 the exact resolution is 853.333333333...x480. You can now see the problem. Rounding to the nearest whole number, I would have 853x480, but now the width is an odd number, and most codecs expect the frame width to be at least a multiple of 2 (sometimes require it to be a multiple of 4, 8, or even 16, particularly like with h264 that has a block width of 8 pixels and a macroblock width of 16 pixels). Rounding to the nearest multiple of 2, the width would be 854. Rounding to the nearest multiple of 4, the width would be 852.

What is the official standard image width, most commonly used by video professionals, for 16:9 aspect ratio video at 480p?

[LMotlow]

SD Video works with mod-8 dimensions. So your 16:9 480p video would be 856x480. If you wanna get really picky about encoding efficiency, you'd stick to mod-16, which means a frame size 848x480. But mod-8 seems to be good enough.


There is no "official" standard width for 480p video because 480p is invalid and out-of-spec for DVD, BluRay, or AVCHD. For any of those encoded formats,. whether with with MPEG for DVD or BluRay, or with h264 for BluRay/AVCHD, the official SD standard is 720x480i flagged for 16:9 display, and is either interlaced or telecined for 27.97 fps NTSC or 25fps PAL.
https://www.videohelp.com/hd#tech
http://forum.doom9.org/showthread.php?t=154533

If you look at all the "standard" widths and heights for official SD and HD sizes, all are mod-16 and mod-8 as well.

[hello_hello]

You could resize to 720x480 with a 16:9 aspect ratio. Same as NTSC DVD video.

The sort of aspect error you're referring to is pretty small.
0.15% if you resize to 852x480 or 0.07% for 854x480.

Or if you crop 2 pixels from one side you could resize to 852x480 with a 0.05% aspect error.

If you really want exactly 16:9, 832x468 is about at close as you'll get to 480p. I mostly use 832x468 for when I want to resize an NTSC DVD to exactly 16:9, but for resizing high definition down to standard definition I'd probably stick to something close to PAL resolution, such as 960x540 or 1024x576, unless loss of resolution really isn't important at all, because it should retain a little more detail than 480p. Once you start resizing to square pixels it doesn't matter what resolution you use. Any player capable of playing video with a resolution greater than DVD (more than 720 pixels wide) will play it regardless, assuming it's capable of playing the video/file type in question. If the output is MKV or MP4 the resolution won't matter. I assume you're using x264 for encoding?

Seems like a good opportunity to mention one of my pet peeves..... not converting the colorimetry from high definition to standard definition when downscaling. If the encoder writes high definition colorimetry to a standard definition video stream, some players will respect it. Others will ignore it and the colours might look a little "off". If you happen to be familar with Avisynth or you're using an Avisynth based GUI, you can convert the colors with the ColorMatrix plugin. ie

LoadPlugin("C:\Program Files\Avisynth Plugins\ColorMatrix.dll")
ColorMatrix(mode="Rec.709->Rec.601", clamp=0)

http://web.missouri.edu/~kes25c/ColorMatrixv25.zip

[newpball]

What is the official standard image width, most commonly used by video professionals, for 16:9 aspect ratio video at 480p?

Video professionals worth their weight in salt would never consider butchering a 1080p video to 480p because of disk space.

[Videogamer555]

SD Video works with mod-8 dimensions. So your 16:9 480p video would be 856x480. If you wanna get really picky about encoding efficiency, you'd stick to mod-16, which means a frame size 848x480. But mod-8 seems to be good enough.


There is no "official" standard width for 480p video because 480p is invalid and out-of-spec for DVD, BluRay, or AVCHD. For any of those encoded formats,. whether with with MPEG for DVD or BluRay, or with h264 for BluRay/AVCHD, the official SD standard is 720x480i flagged for 16:9 display, and is either interlaced or telecined for 27.97 fps NTSC or 25fps PAL.
https://www.videohelp.com/hd#tech
http://forum.doom9.org/showthread.php?t=154533

If you look at all the "standard" widths and heights for official SD and HD sizes, all are mod-16 and mod-8 as well.

However when the the DVD player reads the 720x480 disk flagged for 16:9, the player must then converter 720x480 to 852 or 853 or 854 by 480, prior to displaying it. There must be some standard for that playback conversion by DVD players. And since I'm intending it for playback on a PC not a DVD player, I want to encode it to start with, in the resolution that a DVD player would output when reading a DVD disk that was flagged for 16:9 playback.

[usually_quiet]

The DVD player would still output 720x480 or 704x480 (both are valid for 16:9) and let the TV scale the video, unless the DVD player is one that upscales to 720p or 1080p for HDMI output.

[Videogamer555]

The DVD player would still output 720x480 or 704x480 (both are valid for 16:9) and let the TV scale the video, unless the DVD player is one that upscales to 720p or 1080p for HDMI output.

But how does the TV know to reshape the video frame to 16:9 aspect ratio? The flag for 16:9 doesn't get transmitted to the TV, because the composite video out is an analog connection. It doesn't transmit digital control data like the aspect ratio flag.

[usually_quiet]

The DVD player would still output 720x480 or 704x480 (both are valid for 16:9) and let the TV scale the video, unless the DVD player is one that upscales to 720p or 1080p for HDMI output.

But how does the TV know to reshape the video frame to 16:9 aspect ratio? The flag for 16:9 doesn't get transmitted to the TV, because the composite video out is an analog connection. It doesn't transmit digital control data like the aspect ratio flag.

The player knows what the video's display aspect ratio is, and what aspect ratio the TV uses. For composite output, the DVD player can can add letter boxing to 16:9 video when the TV is 4:3 or use pan-and-scan. It can also squeeze the video a little and add pillar boxing to 4:3 video when the TV is 16:9.

[El Heggunte]

What is the official standard image width, most commonly used by video professionals, for 16:9 aspect ratio video at 480p?

There really is no "official standard image width, most commonly used by video professionals, for 16:9 aspect ratio video at 480p".
You can safely choose 852x480 & 854x480 instead of the often-"recommended" values 856x480 and 848x480.
Any compliant MPEG-4 or VC-1 decoder knows how to deal properly with mod(4) and mod(2) frame dimensions.

[hello_hello]

However when the the DVD player reads the 720x480 disk flagged for 16:9, the player must then converter 720x480 to 852 or 853 or 854 by 480, prior to displaying it. There must be some standard for that playback conversion by DVD players. And since I'm intending it for playback on a PC not a DVD player, I want to encode it to start with, in the resolution that a DVD player would output when reading a DVD disk that was flagged for 16:9 playback.

Well in that case.....

Officially the width of a 16:9 DVD is a tad wider than 1.777777 (16:9) because officially only 704 x480 of the resolution constitutes 16:9, so the "official" way to do it for a DVD would be to resize the 16:9 image to 704x480, add 8 pixels of black bars to each side for 720x480 and set the aspect ratio to 1.82:1.
Your DVD player should use a 1.82:1 aspect ratio for the composite out and the picture will display correctly, so technically if you wanted to be all "official DVD" about it you probably should resize to around 854x480, add black borders each side for a total of 874x480 and encode it that way.
Of course that'd be silly/pointless, but given the "official" DVD spec is 1.82:1 over composite, and 16:9 over HDMI is 1.7777, and HDMI DVD players generally output 1.7777 over HDMI, if you want a resolution a DVD player would use when resizing a 16:9 DVD you'll first have to pick one.

Modern 16:9 DVDs generally use pretty much all the 720x480 resolution for picture and the correct resizing is 1.777777, which means a DVD player with a composite out is likely to stretch the picture a bit.

And don't forget over-scanning. TVs generally overscan by default over HDMI and for composite I think they always do, which is why you don't see those black pixels on the sides using a TV but you do on a PC monitor (it doesn't overscan) so if you want it to look the same on a PC you should crop away between 5% and 10% of the picture from around the edges before you resize to 16:9.

Moving away from the ambiguity of DVD resizing, when it comes to putting anamorphic video in an MP4 or MKV, you should be able to set an exact aspect ratio and it'll be resized to exactly that aspect ratio on playback, rounded to the nearest whole pixel as required. And you can use whatever resolution and aspect ratio your heart desires. 720x480 and 16:9 would display the same way as 340x480 and 16:9.

All software players obey aspect ratios in MP4/MKV files, but it's more hit and miss when it comes to hardware players. For a PC though, you can resize to any resolution you like and set a 16:9 aspect ratio.
Likewise you can resize to any 16:9 square pixel dimensions. 960x540, 640x360 or 832x468 etc and if a hardware player can play the video, it'll display it with the correct aspect ratio. If you want to simulate "DVD 480p" in square pixel resizing, 852x480 or 854x480 is the closest you'll get and the original aspect ratio will remain unchanged (less than 0.1% aspect error). For a PC though, why worry about 480p? Why not just use the lowest 16:9 resolution you can before the loss of picture detail becomes too great?

[hello_hello]

The DVD player would still output 720x480 or 704x480 (both are valid for 16:9) and let the TV scale the video, unless the DVD player is one that upscales to 720p or 1080p for HDMI output.

But how does the TV know to reshape the video frame to 16:9 aspect ratio? The flag for 16:9 doesn't get transmitted to the TV, because the composite video out is an analog connection. It doesn't transmit digital control data like the aspect ratio flag.

A DVD player connected to a modern TV over composite would connect using a 720x480 resolution (or whatever the composite signal is exactly). You can probably use higher resolutions for composite but that'd be standard. The TV knows "NTSC" is always supposed to be 16:9, so it stretches it to fill the screen, unless you put the TV into 4:3 mode (they all have one), in which case it'll resize the image to 4:3 and add black bars down the sides (and it'll also over-scan so some of the image is off the bottom and top of the screen and any crud down the sides is hidden behind the black bars.
It'd be no different than connecting a VCR I'd imagine. It's been a long time since I've used mine, but you'd just connect and tell the TV to be 4:3 if it doesn't do it automatically.

NTSC and PAL resolutions are valid resolutions for a HDMI connection. You don't have to tell the TV what aspect ratio to use unless you want 4:3. It'd assume 720x480 (and 720x576) are 16:9.

All Blurays players are capable of connecting to a TV at 1080p, so if your player connects to the TV at 1080p and you play a 16:9 DVD, the Bluray player would upscale it to 1920x1080. An upscaling DVD player would do the same. Both Bluray players in this house can be set to automatically change the resolution at which they connect to the TV, and they'll both let you set a fixed output resolution in which case they know when they need to upscale.

[usually_quiet]

The player knows what the video's display aspect ratio is, and what aspect ratio the TV uses. For composite output, the DVD player can can add letter boxing to 16:9 video when the TV is 4:3 or use pan-and-scan. It can also squeeze the video a little and add pillar boxing to 4:3 video when the TV is 16:9.

It was late and I was tired when I wrote this. As hello_hello wrote, a 16:9 TV does add the pillar boxing to 4:3 material sent over composite, because the user would set the TV to use 4:3 aspect ratio in such cases, unless the user just doesn't care if everything is distorted.

The DVD player can add letter boxing to a 16:9 video for display on a 4:3 TV. To be sure I was remembering correctly, I just played a DVD that I know contains only 16:9 anamorphic video using my 4:3 CRT TV with a built-in DVD player, and the player added letter boxing.

[hello_hello]

The only time I've actually put a disc in my Bluray player is to test how it works as I encode everything and watch it via a USB hard drive or via my PC, so I thought I'd give it a quick spin with a 4:3 DVD to make sure I got it right. My TV's a Plasma so in 4:3 mode is puts grey pillarboxing down the sides rather than black, so I know when the TVs in 4:3 mode (as opposed to displaying a 4:3 picture in 16:9 mode). At first, I thought the Bluray player was switching the TV into 4:3 mode, and it was messing with my head, until eventually I realised the TV remembers the last used aspect ratio (16:9 or 4:3) for each input resolution, as well as the last aspect ratio used for each resolution per input. Eventually the penny dropped. But......

I tested the above with a Sony Bluray player connected via HDMI, after which I pinched the other player in the house, a Samsung, and tried again and this time the player itself will correct the aspect ratio of 4:3 DVDs so they display as 4:3. I wonder why the Sony player isn't resizing 4:3 DVDs the same way. Maybe a setting? I'll have another look......

Okay, so it turns out the Sony Bluray player can automatically resize 4 :3 DVDs correctly too, without any need to put the TV into 4:3 mode, so I guess when it comes to Bluray players that's probably standard and some of what I wrote before was a load of crap. Although when the TV's in 4:3 mode it overscans. When a player is outputting a 4:3 DVD as 4:3 there appears to be no over-scanning going on, which might be a bad thing if the sides of the picture are particularly "messy".

Tell me how this isn't completely counter-intuitive though?

There's a setting to tell the Sony player the aspect ratio of the TV. It's set to 16:9. There's another setting labelled "Screen Format". When it's highlighted, the "tooltip" says "Set the video with a different aspect ratio than the TV". There's two choices. "Original" and "Fixed Aspect Ratio". How can the second option be the one that allows the player to resize a 4:3 DVD to 4:3 and not the first? It makes no sense to me. Especially as "Original" is the default. I reset the player to check.

Okay, so both Bluray players can output DVDs using the correct aspect ratio without requiring intervention from the TV's 4:3 mode. At least over HDMI. I can't imagine why they wouldn't do the same when connected via the component/composite inputs, but the amount of enthusiasm required to check that exceeds the availability of enthusiasm at the moment. I will check the VCR and whether 4:3 mode is required as it's easy already connected to a TV, but I'll do it tomorrow.

[usually_quiet]

So, what option should Videogamer555 choose for resizing his 1080p video to 480p?

Obviously if he chooses a container or video format that only supports square pixels, he has to choose between 852x480, 854x480, 856x480 or 848x480. <Edit> If it makes any difference, when I looked at the resolution of a 16:9 480p video that I downloaded from YouTube just to see what resolution they used, it was 854x480. <End Edit>

If he chooses a container or video format that supports anamorphic video, 720x480 will work.

If he wants DVD or Blu-Ray compliant video, that gets complicated. The specs require 720x480 resolution, and progressive video is allowed only if it can be played as interlaced at 29.97fps using pull-down flags. This means 480p at 59.97fps or 60fps won't be compliant.

[newpball]

Videogamer555 wrote "And since I'm intending it for playback on a PC not a DVD player..." it is a total non-issue that is discussed here.

The standard were made for man, not man for the standards.

[usually_quiet]

Videogamer555 wrote "And since I'm intending it for playback on a PC not a DVD player..." it is a total non-issue that is discussed here.

The standard were made for man, not man for the standards.

As usual, you only quote what suits you. Videogamer555 asked about what DVD players do. So he must have thought it is relevant to his decision. We answered his questions. It is his video and his decision to make, not yours.

However when the the DVD player reads the 720x480 disk flagged for 16:9, the player must then converter 720x480 to 852 or 853 or 854 by 480, prior to displaying it. There must be some standard for that playback conversion by DVD players. And since I'm intending it for playback on a PC not a DVD player, I want to encode it to start with, in the resolution that a DVD player would output when reading a DVD disk that was flagged for 16:9 playback.

[newpball]

[So he must think it is relevant to his decision.

Since he intends to play this on a PC he is obviously mistaken about that.

Why not help someone who has a mistaken belief about something?

[usually_quiet]

[So he must think it is relevant to his decision.

Since he intends to play this on a PC he is obviously mistaken about that.

Why not help someone who has a mistaken belief about something?

The OP apparently asked the question because he considers DVD video quality to be adequate for his purpose. If he wants to use 720x480 16:9 anamorphic, like a DVD uses, to save more space, he is free to do that as long as the container and codec supports it. If he wants to use square pixels and doesn't mind bigger files, he can certainly use a larger 480p resolution. Again, his choice to make, not yours.

[hello_hello]

I think this is as specific as we got to an explain of the desired output:

However when the the DVD player reads the 720x480 disk flagged for 16:9, the player must then converter 720x480 to 852 or 853 or 854 by 480, prior to displaying it. There must be some standard for that playback conversion by DVD players. And since I'm intending it for playback on a PC not a DVD player, I want to encode it to start with, in the resolution that a DVD player would output when reading a DVD disk that was flagged for 16:9 playback.

The most correct answer, in my opinion, would be 854x480, because if you opened an NTSC 16:9 DVD with a software player such as MPC-HC and displayed it without any further resizing as such, the video width would cover 854 square monitor pixels and it'd be 480 square monitor pixels high. Anything resizing from there would be upscaling or downscaling.

Mind you I do agree. For PC playback the fixation on 480p and DVD resizing seems totally unnecessary.

[usually_quiet]

True. It appears 854x480 is common. I downloaded a video from YouTube to see what they used for 16:9 480p, and it was 854x480.

[manono]

True. It appears 854x480 is common. I downloaded a video from YouTube to see what they used for 16:9 480p, and it was 854x480.

That's just what the guy uploaded, not what YouTube chose as the resolution. For example, here's one that's 848x480:

https://www.youtube.com/watch?v=MiBN0lWIFA8

And to find the resolution of the video you don't have to download it. Right-click the picture and hit 'Stats for nerds'.

[usually_quiet]

True. It appears 854x480 is common. I downloaded a video from YouTube to see what they used for 16:9 480p, and it was 854x480.

That's just what the guy uploaded, not what YouTube chose as the resolution. For example, here's one that's 848x480:

https://www.youtube.com/watch?v=MiBN0lWIFA8

And to find the resolution of the video you don't have to download it. Right-click the picture and hit 'Stats for nerds'.

720p was the highest resolution available to display the video, so isn't it more likely that is what the guy uploaded? If 720p is what the guy uploaded, wouldn't the lower resolutions be what YouTube chose?

[manono]

720p was the highest resolution available to display the video...

Oh, I didn't realize that. Then, yes, you're right that they chose 854x480 for the 480p version.

[jagabo]

Officially the width of a 16:9 DVD is a tad wider than 1.777777 (16:9) because officially only 704 x480 of the resolution constitutes 16:9

Not according to what I've read. I don't have the DVD spec but someone here who did said it referred readers to the MPEG 2 spec regarding aspect ratios. The MPEG 2 spec (which is available online) is quite clear: in the absence of a sequence_display_extension the full frame comprises the indicated display aspect ratio. Of course, we all know that when 4:3 tape sources are put onto DVD they are captured via the ITU spec and the difference between the two specs is ignored. The 720x480 ITU AR frame is written directly to the DVD.

Players I have test follow the ITU spec at the analog outputs, the MPEG 2 spec at the upscaled digital outputs.

[Skiller]

But how does the TV know to reshape the video frame to 16:9 aspect ratio? The flag for 16:9 doesn't get transmitted to the TV, because the composite video out is an analog connection.

No, aspect ratio information can be transmitted even with just a plain Composite video connection (note: can not must): WSS.

Unfortunately not all DVD-Players generate WSS and not all TVs read/obey it.
In absence of WSS saying otherwise, a Composite video signal is assumed to be 4:3, but of course the user may override this.

Okay, so both Bluray players can output DVDs using the correct aspect ratio without requiring intervention from the TV's 4:3 mode. At least over HDMI. I can't imagine why they wouldn't do the same when connected via the component/composite inputs

Because it's not good to do it that way: You lose 25% of horizontal resolution by pillarboxing a 4:3 DVD and outputting it in 576i/480i (or 576p/480p), such as Component, S-Video and Composite. The same happens with non-upscaled HDMI as well, that's probably why there is a "Original" setting – it's there so that the TV can do the job of pillarboxing without losing horizontal resolution. For upscaled output formats there is no loss introduced by having the player do the pillarboxing but you get to see the crud (if any) at the sides because there is no overscan at the sides anymore.

[hello_hello]

Officially the width of a 16:9 DVD is a tad wider than 1.777777 (16:9) because officially only 704 x480 of the resolution constitutes 16:9

Not according to what I've read. I don't have the DVD spec but someone here who did said it referred readers to the MPEG 2 spec regarding aspect ratios. The MPEG 2 spec (which is available online) is quite clear: in the absence of a sequence_display_extension the full frame comprises the indicated display aspect ratio. Of course, we all know that when 4:3 tape sources are put onto DVD they are captured via the ITU spec and the difference between the two specs is ignored. The 720x480 ITU AR frame is written directly to the DVD.

Players I have test follow the ITU spec at the analog outputs, the MPEG 2 spec at the upscaled digital outputs.

You could be right but if there's a sequence_display_extension indicating the aspect ratio, why do no players seem to pay attention to it and resize accordingly?
I know DVD video is mpeg2 but I think the specs for each differ in places (if I recall correctly the default colorimetry for mpeg2 is actually r.709 (in the absence of a sequence_display_extension) while I think for DVDs r.601 is suppoed to be mandatory, but I won't speculate too much in that regard as I don't know for sure.

Of course, we all know that when 4:3 tape sources are put onto DVD they are captured via the ITU spec and the difference between the two specs is ignored. The 720x480 ITU AR frame is written directly to the DVD.

Are you saying most 4:3 DVDs aren't ITU, because I'd be thinking it's exactly the opposite. Are you referring to "professional" 4:3 DVDs or PC capture cards and burning etc.

Anyway for 16:9 DVDs you're saying the "default" is 720x480 and not ITU? You may be correct and I wouldn't argue given I'd be pretty confident most 16:9 DVDs are 720x480 (except maybe very early ones), and Ive come to that conclusion after comparing many of my old DVD encodes with their HD counterparts. Mainly PAL, but I'd be surprised if NTSC is any different. Off the top of my head I can only think of two instances where I've compared the 16:9 DVD to the Bluray version and thought "whoops, I should have used ITU for that one". Both were quite a while ago but I think one was Terminator 2. I can't remember what the other was right now.

Actually having said that......
The BBC seem to like being all "correct" and I've found myself wondering if BBC 16:9 DVDs are still ITU, but I've never been able to do a HD comparison. The BBC might be the exception to the rule though......

[jagabo]

You could be right but if there's a sequence_display_extension indicating the aspect ratio, why do no players seem to pay attention to it and resize accordingly?

I've only ever seen the sequence_display_extension used to indicate the 4:3 DAR is in a 540x480 or 540x576 portion of the 720 pixel wide frame. That implies the full 720 pixels is exactly 16:9 (4/3*720/540) DAR. I've never seen one indicate the DAR is in a 704 sub frame.

Are you saying most 4:3 DVDs aren't ITU

I'm saying the video on many (probably most) of those DVDs were digitized following the ITU spec. When they were written to DVD the difference between the ITU and MPEG 2 specs was ignored. So the DVDs are ITU, apparently in violation of the DVD spec. And as I indicated earlier, even many players are schizophrenic about the issue, putting out ITU DAR at the SD composite output and MPEG2 DAR at the upscaled HDMI output. So apparently nobody in the industry cares about the difference.

Anyway for 16:9 DVDs you're saying the "default" is 720x480 and not ITU?

I'd say you have to approach each DVD individually to determine the aspect ratio -- if you care. It may follow the ITU spec or the MPEG 2 spec. And occasionally it's completely out of either spec.

[Skiller]

And as I indicated earlier, even many players are schizophrenic about the issue, putting out ITU DAR at the SD composite output and MPEG2 DAR at the upscaled HDMI output.

Indeed. Analog SD outputs always follow ITU because there is simply no other way of converting a digital SD frame to an analog signal (and vice versa). The encoded frame is converted by the DVD-player's DAC which runs at 13.5 Mhz (or rather multiples of 13.5 for oversampling) and this will always result in an analog signal where a non-ITU source frame comes out wider than defined by analog signal standards (52µs = active picture area for PAL; 720÷13.5 = 53.333µs and is too wide). So it's perfectly valid to say that for SD analog output a non-ITU source frame is always incorrect, regardless of what the MPEG2 spec says because ITU is the interface between digital and analog.

This raises a problem, of course, as mentioned DVD-players tend to stick to straight 4:3 or 16:9 resizing when upscaling, and who knows what standard LCD and Plasma TVs actually stick to when they upscale a Composite signal or SD HDMI...

In short, it's a mess – but it really wasn't until upscaling and fixed pixel displays came along (call me "stuffy").

[jagabo]

Analog SD outputs always follow ITU because there is simply no other way of converting a digital SD frame to an analog signal (and vice versa). The encoded frame is converted by the DVD-player's DAC which runs at 13.5 Mhz

I agree with you that most (all?) modern players run the DAC at 13.5 MHz because they use off-the-shelf parts. But that doesn't mean there's no other way. The analog signal could be sampled with as many or as few samples as one wants. The ITU just settled on 13.5 MHz. There's no reason someone couldn't run their DAC at ~13.8 MHz so that the full 720 pixel width frame contained the 4:3 image.