aspect ratio conversion.... for real?

[derwildemann]

Some time ago I bought a 3D goggle for my iPhone. I thought that it would enable me to watch 3D movies which what I was searching for, but the purpose of this device is just to play some 3D virtual games or stuff like it.

I had the device for almost a year and then I had an idea. A 3D HSBS movie plays on a normal 16 by 9 screen dividing the screen in 2 half screens, each 8 by 9 being the left part for the left eye and the right for the right eye.

With the VLC command line interface I could play the 3D HSBS video in 32 by 9 which gives the correct aspect ratio of both half screens. Unfortunately there in not any video player app for my phone that allows to do this.

So I checked for an application that could convert a video from 16 by 9 to 32 by 9. I found one in VirtualDub.

The downside, it takes even my powerful computer more than an hour to convert a 90 minutes video. In the past I used mkvmerge to transcode mp4 movies into mkv. A 90 minutes video takes just 3 minutes to convert. And there is even a feature in mkvmerge (format specific options) that made me think I could do this aspect ration thing too but that didn't work. I'm using version 4.9.1, maybe a newer version would do this, I don't know.

What I need is to physically transform a 16 by 9 aspect video into a 32 by 9. So if the frame size of the original video is 1920 by 1080, then the outcome should have 1920 by 540.

I haven't figured out how to do that. I might do something wrong (format specific options) but the resulting video always keeps the original aspect ratio.... maybe not totally but never even close to 32 by 9.

I believe this feature to be awesome.... you'll be able to watch a 3D movie w/o any special glasses to separate left from right....

[Brad]

Mkvmerge does not transcode. It's fast because all it does is copy the existing data into a new container. The speed is limited by your HDD/SSD storage.

Resizing the stored video data, rather than just flagging a new aspect ratio that the player may ignore, requires actual transcoding. Each frame is decompressed, altered as you wish, then recompressed. The speed is limited by your CPU.

[Cornucopia]

Do you know how to cross your eyes, or how to decorrellate your eyes' accommodation and focus link so that you can view parallel? If not, you won't be able to correctly view it as S3D unaided. Google has, AFAIK, an iPhone viewing adapter with lenses to help, and I think it already does the AR correction for you.

Scott

[derwildemann]

Do you know how to cross your eyes, or how to decorrellate your eyes' accommodation and focus link so that you can view parallel? If not, you won't be able to correctly view it as S3D unaided. Google has, AFAIK, an iPhone viewing adapter with lenses to help, and I think it already does the AR correction for you.

Scott

As I said in my original post, I used VirtualDub to transcode the original 16 by 9 video to 32 by 9. It took my computer some 90 minutes but the result is everything I wanted to achieve, and yes.... I can watch it with the cardboard 3D goggle in true 3D, guess you were referring to this mentioning the Google device. There are, in fact, lots of similar devices like that on the market, mine is called "beenoculos". So if mkvmerge doesn't do it, ok, got it, don't like it but have to live with it.... Would be nice though, if perhaps VLC could update their iPhone app to be able to freely choose the aspect ratio when playing a movie.... that's not possible at this stage....

cheers

[jagabo]

You might be able to change the display aspect ratio without reencoding. Just use the MP4 container's aspect ratio flag when you remux. The question is whether or not the player on you iphone will honor the flag.

[derwildemann]

You might be able to change the display aspect ratio without reencoding. Just use the MP4 container's aspect ratio flag when you remux. The question is whether or not the player on you iphone will honor the flag.

may I ask you to explain? sounds greek to me....

[jagabo]

Open your file in Mkvtoolnix. Highlight the video track. In the options Set Aspect Ratio to 32/9. Save. You can do the same with some MP4 muxers if you need mp4 instead of mkv.

[derwildemann]

Open your file in Mkvtoolnix. Highlight the video track. In the options Set Aspect Ratio to 32/9. Save. You can do the same with some MP4 muxers if you need mp4 instead of mkv.

I guess you are talking about mkvmerge? if so, I had tried that already. in fact it doesn't seem to matter at all what you choose in the aspect ratio field.... the outcome is exactly as the source, no idea what that field should do...

[jagabo]

Open your file in Mkvtoolnix. Highlight the video track. In the options Set Aspect Ratio to 32/9. Save. You can do the same with some MP4 muxers if you need mp4 instead of mkv.

I guess you are talking about mkvmerge? if so, I had tried that already. in fact it doesn't seem to matter at all what you choose in the aspect ratio field.... the outcome is exactly as the source, no idea what that field should do...

It adds a flag to the MKV header telling the player to play the file at 32:9. Unfortunately, your player is ignoring the flag. You might try the same thing with MP4. Maybe the player will pay attention to the flag there. If not, you'll have to reencode with a horizontal stretch.

[Baldrick]

And you can try mymp4boxgui to change the aspect ratio with a mp4. Add the video, right click on the video track and choose PAR->Custom 32:9 . Click Save as and last Mux.

[derwildemann]

And you can try mymp4boxgui to change the aspect ratio with a mp4. Add the video, right click on the video track and choose PAR->Custom 32:9 . Click Save as and last Mux.

thanks for the hint.... dindn't work either however....

[jagabo]

One last thing you can try; demux the video track and use a program like h.264 AR Changer to change the AR of the video stream. Then mux into the container you want. I recommend you also set the container AR flag. Note that the PAR or SAR should be 2:1. The DAR is 32:9.

DAR = SAR * FAR

DAR = Display Aspect Ratio (the final shape of the picture)
SAR = Sample Aspect Ratio (the spacing between the samples)
FAR = Frame Aspect Ratio (the frame dimensions)