Exporting Video for YouTube: Pixel Aspect Ratio Basics

The article just deals with Pixel Aspect Ratios (PAR). If you want an overview of all export settings, you can go to this page: Exporting HD Video for YouTube

Are you exporting digital video, want to upload it to a video sharing site and wondering what resolution and pixel aspect ratio to choose? This article offers some suggestions. Basically, when you are exporting and/or uploading your video, you are looking for a pixel aspect ration of 1:1 (known as square pixels). Luckily, almost everyone is using High Definition (HD) video these days, and choosing pixel aspect ratios and resolution for HD video is easy; it only becomes difficult if you need to convert or export Standard Definition (SD) formats

1. Terminology; PAR, DAR, Pixel Dimensions

Digital images are made of pixels—tiny little squares or rectangles. If you zoom in on a digital image you will start to see the individual solid-color pixels that make up the image. The more pixels there are in an image, the higher it’s resolution.

  1. Display Aspect Ratio = The ratio of the width to the height of the entire image (widescreen is 16:9, non-widescreen is 4:3)
  2. Pixel Aspect Ratio = The ratio of the width to the height of each pixel that makes up the image. A square pixel has a pixel aspect ration of 1:1
  3. Pixel Dimensions (i.e., resolution) = The width and height of the image measured in terms of pixels (e.g, 1280 x 720). In this article, I will refer to pixel dimensions as ‘resolution’.
  4. Anamorphic Video: The pixels used to create the image are rectangular.

 

2. Pixel Aspect Ratios and Resolutions for HD Video

This is the simple one, so lets get this out of the way first. For HD video, it doesn’t matter if you are using PAL or NTSC when choosing pixel aspect ratio and resolution. You have the following choices:

  1. Full HD video at 1920 x 1080 (square pixels): you can export it at 1920 x 1080 or you can downscale it to 1280 x 720 (also square pixels) if you are concerned about file size.
  2. HD video at 1280 x 720 (square pixels): export it at 1280 x 720.
  3. Anamorphic HD video (1440 x 1080) and want to play the video on a media player or make a DVD: you can export your video at that resolution without changing the pixel aspect ratio.
  4. Anamorphic HD video (1440 x 1080) and you want to upload the video to a video site: you can change the resolution to 1280 x 720 and change the pixel aspect ratio to square pixels. You can also just leave the resolution and pixel aspect ratio as they are and let the video site do the transformation for you. You will likely end up with a video that can viewed at a resolution 1280 x 720 (YouTube’s 720p option), though the quality would probably be better if you did the downscaling yourself.

Anamorphic HD video (1440 x 1080) uses fewer pixels, but because the pixels are rectangular, the image is stretched out so that it appears as large as higher quality Full HD video.

 

3. Standard Definition: Pixel Aspect Ratio Problems and Solutions

Computer monitors display images using square pixels (i.e., a pixel aspect ratio of 1:1) and video-sharing sites like Vimeo and Youtube prefer uploaded videos to be in formats with square pixels. However, standard definition video formats like PAL and NTSC, which are based on their respective television broadcast formats, produce images using rectangular pixels. For example, PAL video (standard definition, non-widescreen) has a display aspect ratio of 4:3, a pixel aspect ratio of 12:11 and pixel dimensions of 720×576.

The Good News
Almost all computer media players will happily play video with rectangular pixels so that they look fine on a computer monitor. Web uploading sites like YouTube will also automatically convert your video into a format using square pixels when transcoding your video.

  • Example 1: If you upload an anamorphic HD Pal Video (1440 x 1080), YouTube will convert it into a 1280 x 720 HD video with a pixel aspect ratio of 1:1 (YouTube’s 720p viewing option).
  • Example 2: If you upload a PAL SD Video (720 x 576), YouTube will convert it into a 640 x 480 video with a pixel aspect ratio of 1:1 (YouTube’s 480p viewing option).

 

The Bad News
You may not like the conversion job done by YouTube (though I think their transcoder is much improved). Also, video uploaded to some sites like Vimeo tend to work work better if they are uploaded in a standard square pixel format.

 

Solutions
If you are working with:

  1. Standard definition video (PAL or NTSC) and want to make a DVD or play the video on your computer, just go with the default settings (i.e., don’t change the resolution or aspect ratios).
  2. Standard definition video (PAL or NTSC) and want to to upload it to a video site, you can let the video site try to convert the aspect ratios, or you can do it yourself. This is tricky, especially when working with widescreen formats, so I would suggest that you try the default settings first (Just select a preset (e.g., PAL-DV, PAL Widescreen-DV, NTSC-DV, etc.) in your video editing or exporting programme, don’t change the resolution or aspect ratios) and see how things turn out once your video is uploaded . If you don’t like the results, you can consider the following suggestions:

PAL 720 x 576 (non-widescreen)
You want a display aspect ratio of 4:3 and pixel aspect ratio of 1:1. Change the pixel aspect ratio to ‘square pixels’, crop some pixels of each side (Premiere Pro will crop a total of 17 pixels off the left and right sides; for example, 8 from the the left and 9 from the right side. Cropping 16 pixels might be enough, so you can test out both options.) and export the video at a resolution of 704×528 or 640×480. If you don’t crop the video, when you export it, your video exporting programme will likely either add black bars to the top and bottom of the video (known as letter-boxing) or will stretch out the video, making objects appear slightly distorted. Letter-boxed video will look OK on your computer monitor, but when you upload it to YouTube, you will also get black bars on the side. Your video will be smaller than it should be and will surrounded by black bars on all four sides (ugly!).

NTSC 720×480 (non-widescreen)
You want a display aspect ratio of 4:3 and pixel aspect ratio of 1:1. Change the pixel aspect ratio to ‘square pixels’, crop a total of around 15 pixels off each side (e.g., 8 from the the left and 7 from the right side) and export the video at a resolution of 704×528 or 640×480 (exporting at the latter resolution will create a smaller video, but it will match YouTube’s 480p pixel dimensions).

PAL Widescreen (720 x 576) and NTSC Widescreen (720 x 480)
The solutions are very problematic and may vary depending on the camera that you are using and the website you are uploading to, so you will need to experiment with different resolutions when exporting (or you may just keep the default resolution and pixel aspect ratio and hope for the best). I would suggest experimenting by exporting a short clip (e.g., several seconds long) using different resolutions and seeing which one works best. Basically, you are looking to change the pixel aspect ratio to ‘square pixels’ (i.e., 1:1) and change the resolution so that the display aspect ration is 16:9.

You can try downsampling to 640 x 360  or 512 × 288 (or 524 x 288 for PAL video, according to some websites), but the video will then be quite small. You can also upsample to 1024 x 576 (or 1048 x 576 according to some websites). It is even possible to upsample it to HD at 1280×720. Upsampling (increasing the resolution of an image or video) is generally a bad idea because you are not really increasing the resolution, you are just making the image dimensions bigger (To understand this, try zooming in on a photo in your computer. The image on the monitor will get larger, but after a while the pixels that make up the image become more and more obvious). I would only suggest using this upsampling method as a last resort, but it is one method of dealing with PAR problems when exporting video in widescreen formats.

I did this lind of upsampling (up to 1280 x 720) for one video and it looked OK on YouTube (though admittedly the video ended up with a ‘soft’ look); what this approach did was to get YouTube’s transcoder to accept and convert the video into an appropriate standard definition widescreen format without any letter-boxing.

Fot NTSC Video, you can try  the following dimensions: 960 x 540, 853 × 480, 854 x 480 (recommended by many websites and the closest to a 16:9 widescreen ratio) or 856 x 480 (the composition settings After Effects uses for NTSC widescreen). You may need to crop pixels off the side (try a total of around 15 pixels of the image) when exporting it. 

Why are there sometimes two different sets of dimensions for the width (e.g., 1048 or 1024; 524 or 512)? It depends on how your camcorder interprets the widescreen display aspect ratio—that is, whether or not it follows the traditional PAL format in which extra pixels are added to either side of the image.

I find trying to get widescreen formats, standard definition and square pixels to get along with one another is very problematic. I would suggest that if you want to work in widescreen, go for HD video. Life becomes so much easier. If you are working with Full HD video your source video, editing project settings and exported video will use square pixels. Even if you are working with anamorphic HD, it is easy to export it at 1280 x 720 HD.

Note: Video transcoders work better when your dimensions are multiples of 16. (e.g., 1920, 1280, 720, 704, 640, 524, 480, 360, etc.). YouTube’s transcoder prefers these standard pixel dimensions and but can usually handle other dimensions (like 853 x 480).
Let me know how these settings work or if there are any problems with the suggestions.

My Other Articles on Video Editing

 


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5 thoughts on “Exporting Video for YouTube: Pixel Aspect Ratio Basics

  1. Thanks for your article about converting SD widescreen for youtube and Vimeo.
    I specially appreciate you trying to help us Pal users. As you noted: “…trying to get widescreen formats, standard definition and square pixels to get long with one another is very problematic”, indeed, and the Pal format makes it even more so.

    I first tried exporting from PP6 direct to H264, using the Pal D1DV 16:9 presets, it was clean enough so I uploaded it to youtube but the out-coming results were very poor. It was widescreen alright, but the sharpness and colors were terrible, much worse then with Pal 4:3 DV material converted to H264, Mpeg4 or WM, and uploaded to YT.

    Then I tried to upscale the DV file in PP6, then I converted it to a H2641280 x 720p file and uploaded it to YT, but it was just as bad!

    I know there are several issues involved here… YT converters prefers NTSC, 25 fps progressive, square pixels, and finally it is said that multiples of 16 give better results…

    So should I first convert my Pal DV file to a NTSC DV file, then convert this anamorphic 720 x 480 NTSC DV file to H264 square pixels? If so, what would be the best size? I would like to keep as much of the original image size and quality as it’s been shot with 1/2 inch 3 ccd pro DV camera and it is very good…

    And also, what size should I use? And do both numbers have to be multiple of 16?

    - 720 x 405 (405 is not multiple of 16, does it matter? )
    - 720 x 480 (again not a multiple of 16)
    - 852 x 480 (That seems good but 852 is again not a multiple of 16)
    - 1024 x 576 (better maybe, as both numbers are a multiple of 16, and the ratio is right?).

    On the behalf of the Pal community, I thank you for any additional help and advice.
    Raphael

  2. As someone stuggling to come up to speed on what to me, and my generation, are highly complex issues, never anticipated to be needed by our “demographic” (over 50), I cannot thank you enough for so clearly explaining these aspect ratio issues.

    I am a children’s author, and need to “join” the crowd and get my book out on a DVD and uploaded to YouTube.- Or, I will not be able to compete and my “lifes work” will not be seen-especially since it is geared to ages 3-8 yrs old, and therefore their parents are likely to be utilizing YouTube, and DVD as the format of choice, not an “old fashioned” printed book. I cannot thank you enough! Great job, with the unintended consequences of helping the “elders” to pass on their stories to the younger generations. (Now I have to go look up what a “tag” is.) Very best regards, Una King

  3. Pingback: Exporting HD Video for YouTube (Premiere Pro) | Longzijun

  4. Pingback: Choosing Premiere Pro Project Settings for HD Video | Longzijun

  5. Pingback: Upscaling or Upsizing Video? | GLJ Media Group

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