Keeping the Same Aspect Ratio as the Source

[clark]

How can I keep the same aspect ratio of the source material, when changing either the width or the height of the Video Size? I feel like I must be doing a lot of unnecessary math simply because I do not see a way to toggle to keep the aspect ratio, or at least some sort of calculator. Where can I even see what the original Video size of the source is in ffmpegX?

[major]

There are usually only 3 possibilities (unless you're creating a DVD, where there are only 2 possibilities). They should be set with the "Autosize" popup menu, which -is- a calculator.

a) 4:3 aspect (normal TV)
b) 16:9 aspect (widescreen TV)
c) 2.35:1 aspect (feature movie, even wider than TV)

If your source looks about square, choose a).
If your source is a widescreen DVD, choose b).
If your source is a feature movie without black bars, choose c).

No other math to use.

[bluecrab347]

I've found that a 2.35 aspect ratio source doesn't produce the identical output file, despite the settings. My info from the progress window says:

Seems that stream 0 comes from film source: 30000.00 (30000/1) -> 24.00 (24/1)
Input #0, avi, from '/Users/actor/Movies/filename.avi':
Duration: 01:34:40.3, start: 0.000000, bitrate: 922 kb/s
Stream #0.0, 24.00 fps(r): Video: mpeg4, yuv420p, 672x272
Stream #0.1: Audio: mp3, 48000 Hz, stereo, 32 kb/s
Output #0, vob, to '/Users/actor/Movies/filename.avi.ff':
Stream #0.0, 23.98 fps(c): Video: mpeg2video, yuv420p, 672x272, q=2-15, 922 kb/s
Stream #0.1: Audio: mp3, 48000 Hz, stereo, 128 kb/s
Stream mapping:
Stream #0.0 -> #0.0
Stream #0.1 -> #0.1

I chose the same video size, autosize and bitrate as the original, but the video observed in Mplayer with the Preview button was definitely 4:3. Is it not possible to achieve the same aspect ratio? I want to make a DVD; why does this limit my aspect ratio?

Does the output and source frame rates not being equal have any significance in this problem? What frame rate should I have chosen?

[Case]

DVD can be 4:3 or 16:9. To get 2.35:1 in a 16:9 frame, you'll have to letterbox, i.e. add black on top and bottom to make it 16:9. (This is how commercial DVDs work, too.) There is a 'Letterbox' checkbox in Options.

DVD is 720x480 (NTSC) and these numbers are unrelated to aspect ratio; forcing 672x272 would make an invalid size for DVD. Use the 'DVD 16:9' Autosize to get the correct video size filled in. This will also set the output to play as 16:9.

For 23.976 fps DVDs, check the "Set 3:2" checkbox in Options for smoother playback. Read up on '3:2 pulldown' for technical details.

Your DivX AVI has a low bitrate (922 kbps) to get nice small files, but DVD can't go that low. Use the 'Best' button in the bitrate calculator to get a "high enough" value.

And you can't have mp3 for the audio stream on DVD. Use mp2 or ac3.

Framerate does not relate to the aspect ratio. If you're not specifically aiming for a framerate conversion, then leave the value as ffmpegX put it there, as that is the "best valid value" based on your source file.

[bluecrab347]

Case, thank you for a very complete response to this newbie. I've read about some of this before, including just discovering an earlier post of yours on letterboxing, but seldom is it as completely described as you have.

However, I cannot find a "Set 3:2" checkbox in Options. I'm encoding with ffmpeg and running ffmpegX 0.0.9x r2.

[Case]

DVD mpeg2enc does have a "Set 3:2" option,
while DVD ffmpeg doesn't have it.

Use the other preset.

[bluecrab347]

I haven't been able to correctly install ffmpegX, so I don't have that encoder available to me. I don't wish to cross post, so I haven't raised it here, but suffice it to say that I'm having the problem which seems common to many, and I haven't seen a solution for it yet.

[Case]

• You could fix mpeg2enc.
• Or, you could ignore the 3:2 pulldown and see how your player handles it.
• Or, you can encode with ffmpeg and manually add a pulldown. When encoding, uncheck Author as DVD, as you will add some steps before authoring. When encoding is done, you'll have an .mpg file. Demux that using Tools>Demux. Now you have separate video (m2v) and audio (mp2 or ac3) streams. Add a 3:2 pulldown to the video file using Tools>Pull. Now mux them back together using Tools>Mux. Check the Author as DVD box there to get a VIDEO_TS folder which you can burn.

[bluecrab347]

Case, I tried your third option, because I already knew the second didn't work. That third option worked beautifully on the test split file I read about in another of your posts in May 06; I could hear audio, the aspect ratio was as desired and there was no jerkiness on the video in DVD Player.

What I don't understand is how newbies are supposed to know how to operate ffmpegx; so many features are not documented or explained in the online help. Is there another source besides scouring the forum? For example, I didn't understand why one split a file, but I can see now how it saves time. The online Options page doesn't refer to Authoring a DVD at all for the ffmpeg encoder, although that is a checkbox on my Options tab. How does one know that demux and mux are possible, or what they do?

I'm not trying to be rude or ungrateful for your thoughtful and thorough help, but it is difficult to find answers, and a comprehensive description of the tools that ffmpegX packages would be very helpful.