Desired aspect ratio can not be achieved

[vide]

Hi,

I have a 1280x720 video file source.

The desired outcome is 640x388 pixels and 16:9 aspect ratio.

When i set the output dimensions to 640x388 and produce the video. MediaInfo software indicates that aspect ratio is 1.649.

How can i achieve both desired aspect ratio and dimensions?

Thanks.

[Cornucopia]

Do the math: (assuming square pixels) 1280 / 720 = 1.77777 (aka 16:9), 640 / 388 = 1.649. Just like it reports.

The only way to achieve both the AR and the dimensions with the resolutions given is to crop/pad. IIWY, I'd use 640 / 1.7777777777 = 360 and pad black top & bottom 14 each to give 388.

Scott

[vide]

Thank you very much for quick and great answer.

640x360 video is 16:9. That's ok. However, adding black bars and making it 640x388 will make it 1.649 again. Right?

[poisondeathray]

Why is the desired outcome 640x388 ? What is the destination goal?



16:9 would normally be encoded as 640x360 with "square pixels"

16/9 = 640/360 x 1/1



TO use "non square pixels" with those dimensions, you would need to use --sar 1078:1000 (SAR is "sample aspect ratio, but it's also called "PAR" or pixel aspect ratio - just different naming conventions. You can think of it as the width:height of the "stretched" pixels upon playback ). But some devices, destinations (e.g. web/flash) do not support this

16/9 ~= 640/388 x 1078/1000

[vide]

The customer wants video at that dimensions which is the size of space for the video in his website. Also he wants it to be 16:9 (I dont know why)

[poisondeathray]

It won't work for a website (you can only use "square pixels")

Clarify what is required . He probably meant size including the player front end (with the control underneath and the GUI) . I suspect the 28 vertical pixels are probably for the seek bar/ controls etc....

Otherwise you have to letterbox it (top and bottom black borders) as Scott suggested . In that case, mediainfo won't read the real aspect ratio (because it won't take into account the letterbox)

[vide]

Thank you for your clear explanations. One last thing;

How do you calculate SAR? I mean you said 1078:1000, how did you get those numbers? (So i can use the formula in the future)
Thanks.

[poisondeathray]

How do you calculate SAR? I mean you said 1078:1000, how did you get those numbers? (So i can use the formula in the future)

It's just math, solving for equation

DAR = FAR x SAR

Display Aspect Ratio = Frame Aspect Ratio x Sample Aspect Ratio

(Beware: these terms can have different naming conventions. Sometimes FAR is called Storage Aspect Ratio... so it can be confusing (since "SAR" can mean sample aspect ratio as well). The reason is MPEG2 vs. MPEG4 terminology and the people that made the standards decided to change all the names for MPEG4.... anyways....)

FAR can be thought as the width:height of the encoded frame dimensions
SAR can be thought as the width:height of the pixels

So:

16/9 = 640/388 x SAR

Solving for SAR:
SAR = 16/9 x 388/640 = 1.07777777......

So the fraction approximation of 1.0777777 is 1078/1000. You can use more places if you want