"Decode with QT", resizing plus mplayer/Preview issues

[konstantinos]

Hello, I've started using ffmpegX and I have some questions where I would like your assistance.

(Please note that I'm a complete newbie when it comes to video conversion techniques/terminology/etc.)

1.a. When using the ffmpeg engine, what does the "Decode with QT" option (found in "Options") actualy mean/do?

1.b. Similarly, I can't quite figure out what to do with the whole letterbox/resizing issue. I don't have a 16:9 TV set (it's the standard 4:3); while fullscreen (read: no black bars) would be nice, I think that changing the ratio may result in part of the picture getting lost or something? So, I think I'd like to keep the original image ratio as untouched as possible, if touching it means things may get lost along the way. So how do I proceed with the letterbox option?

2.a. I've made sure to install the mencoder, mplayer and mpeg2end binaries. The "Preview" button found under "Info | Play" (screenshot) won't work at all (non-responsive) -- is that normal?

2.b. The "Play" button works but when I close the mplayer window that pops up, I'm greeted with a "The application mplayer quit unexpectedly" window -- screenshot. This is the log that comes up if I click on the "Report..." button.

2.c. Similarly, if I click the "Preview" button found in the "Filters" tab (screenshot -- the only functioning "Preview" button), when I close the resulting mplayer window I get this message.

Then I'm greeted with the same "The application mplayer quit unexpectedly" window as in (2.b.) and this is the log that comes up if I click on the "Report..." button.

Any idea what's wrong? How do I fix these errors?

Thank you very much for your help in advance. I appreciate it!

[Case]

2b/2c. One should quit mplayer by using the <Return>, <q> or <ESC> key. It will then stop/close without any error messages.

[rumplestiltskin]

Decode with QuickTime - means exactly that; best to use it if QT Player can play the source video correctly.

Letterbox/resizing issue - Use the same ratio as the source. Let's say the source video is 720x352 and you'd like to play it through your iPod to your standard definition TV. That's 640 pixels wide so you would calculate as follows:

desired width / source width * original height = desired height

Plug in the numbers and we get:

640 / 720 * 352 = 313

We need to use a multiple of 16 for both width and height. The 640 width is okay but 313 isn't good; so we can choose either 304 or 320. As 313 is closer to 320 than 304, we'll choose that. So set the width to 640 and the height to 320.

The "letterboxing" will appear (approximately 80 pixels top and 80 on the bottom).

There are many options and many workarounds to transcode some sources to some destination formats. You've found the right forum, however, to ask your questions.

[konstantinos]

2b/2c. One should quit mplayer by using the <Return>, <q> or <ESC> key. It will then stop/close without any error messages.

Ah, I see now. Thank you for that one, sir.

Any idea why the "Preview" button under "Info|Play" (screenshot) won't work at all when pressed? Is this normal?

[konstantinos]

rumplestiltskin: first of all, thank you for taking the time to help me and write such a detailed answer. Please allow me for some follow-up questions.

Decode with QuickTime - means exactly that; best to use it if QT Player can play the source video correctly.

OK. Still don't get what's the fuss with QuickTime decoding, but I don't think I'm interested anyway. "Best to use it if QT Player can play the source video correctly" is what I'm keeping from here -- handy and practical advice.

RE: Letterbox/resizing issue: I'm still confused actually. I understand the logic behind wanting to set the width in the target file's resolution to 640 (and from there figuring out what to do with the height) but I don't know how to deal with some of ffmpegX's automatic decisions.

Let's work with this scenario: a DivX that I want to convert to DVD (ffmpeg) so that my regular DVD player can read it -- it's intended for my 4:3 TV.

Way of thinking:
1. I don't like black bars, but most importantly:
2. I don't want to mess with ratios and lose parts of the picture so:
Ratio preservation > black bars, in my book.

Here's what happens if I load a source file to ffmpegX:

Example #1:
- The resolution of the source file is: 524x274.
- I choose "DVD (ffmpeg)" as the target format.
- The resolution of the target file is automatically set to: 720x576 (and there's a "no crop" note too).

Am I supposed to change this? Do I have to mess with the "Video parameters" in the "Video"tab? What should "Video Size:" and "Autosize:" be set to? Also, in the "Options" tab, assuming I have selected "Decode with QT", should I have "Letterbox" checked or not?

Example #2:
- Resolution of source file: 624x352
- Resolution of target file: 624x352

Same questions as above, I guess.

[Case]

Any idea why the "Preview" button under "Info|Play" won't work at all when pressed? Is this normal?

A special kind of preview, to have a look at the part that's already converted. From the website:

• Click this button to preview the converted movie while it's still encoding. In mpeg-2 encoding, audio is encoded after the whole video has been encoded, so the video will preview silent.

[Case]

OK. Still don't get what's the fuss with QuickTime decoding, but I don't think I'm interested anyway.

Any source file has to be decoded for conversion. In ffmpegX, this means either decoded by QuickTime, by ffmpeg or by mplayer. The results from these decoders are not equal; so, you may prefer one over the other on quality. Or prefer one on speed. Or one decoder can decode something that the others can't. Or one has special features that you may want to use. Or one has a really good timing architecture, which helps keeping video and audio in sync.
It's like picking the right tool for the job from the toolbox. Sometimes that means picking QuickTime.
But... because of the modular design of QuickTime (plugins/components) you may need to install some extras for QuickTime decoding to work correctly. 'Cause if QT can't decode a source file without said component, then the conversion will fail, if Decode with QT is selected.

[konstantinos]

RE: Preview: Ah, I had missed that one. Thanks!

RE: QT decoding: excellent explanation, got it now!

Thank you for taking the time to explain these things Case, I appreciate it.

Now, only thing left to figure out is that ratio thing...

[rumplestiltskin]

Add'l re: Decode with QT

I have an AVI with AC3 audio (why people do this is beyond me). Anyway, QT Player would play it (because I do have the appropriate codec). If I try to use MPEG Streamclip to do the transcoding (to H264 for iPod), that app doesn't "hear" the audio (which is strange because it uses QT to do its decoding).

So I dropped the AVI into ffmpegX and deselected the Decode with QT checkbox (figuring that ffmpegX wouldn't be able to "hear" it either). I ended up with video that played at double-speed but normal speed audio; two hours of audio but one hour of white screen.

I then checked the Decode... checkbox and ran it through again. This time ffmpegX did the transcode properly. All audio perfectly sync'd with the video (and at normal speed).

All of the above is my parable about why using the Decode with QT checkbox is good to use whenever possible.

[konstantinos]

Excellent, the "QT decoding" issue is definitely understood now.

Any help with the ratio thing? (Check this post where I write my questions in detail.)

Thanks!

[rumplestiltskin]

The "Autosize" popup menu is simply there as a convenience; pick one choice and the ratio is set automatically. However, it may not be correct; your original ratio (assuming it's correct) may/should be set manually (using the formula I posted earlier) if the Autosize function results in a wrong ratio.

Frankly, I never use the Autosize menu. I do the math and set the height/width as needed.

[konstantinos]

OK, I'm not making any sense at all here.

So, if I disregard your advice and go as with example #1 (720x576) what will the end result be?

Similarly, if I choose the 4:3 ratio from "Autosize" why do I get 720x544 and not 640x336 as your method suggests?

And finally, when do I check the "letterbox" option next to "QT decoding"?

Ah! Too! Many! Questions!

(Whether or not you continue to help me, thank you for your help so far, guys.)

[Case]

If your source file is 524x274, then you've got an aspect ratio of 1.91:1 (slightly wider than 16:9). If your source file is 624x352, then you've got an aspect ratio of 1.77:1 (16:9).

Some target formats have a fixed video size, like DVD, SVCD, VCD and DV. E.g. most DVDs are 720x576 for PAL regions, or 720x480 for NTSC regions. This is true for 16:9 aspect ratio as well as 4:3. This is done by using rectangular pixels, not square ones (as most desktop movie files have).

If your source movie has an aspect ratio that isn't 16:9 or 4:3, and you're converting to DVD, then you'll have to make the video size 16:9 or 4:3 by cropping or adding black to the movie . The latter is referred to as letterboxing.

If you're converting to DVD, then you'll have to set the Autosize to 'DVD' (=DVD 4:3) or 'DVD 16:9', and not use any of the other Autosize aspect ratio settings, as that would make invalid files for DVD.

If you use the Decode with QT option, then you can letterbox by using that checkbox, without having to calculate how many extra black pixels are needed. QuickTime does that for you.
If you decode with ffmpeg and you want to letterbox, then you'll have to use the letterbox fields in the Filters tab, and calculate the amount of padding yourself.

Example. Your source file is 640x272. Aspect ratio is 640:272=2.35:1. If you convert this to DVD 16:9, then you'll need to letterbox. QuickTime's letterboxing will add a black bars on top and at the bottom of 12.5% of the total height, which is 58 and 60 pixels for NTSC (it needs to be an even number), to get a 2.35:1 picture in a 16:9 frame. Just by using the checkbox.

Hope this helps.

[rumplestiltskin]

I just ignore the Autosize menu and set my own sizes taking into account the original ratio plus the "rule of 16's".

[konstantinos]

OK, I've read and re-read your message Case, and thank you very much for taking the time to write it. Some things just don't make sense here, probably because I'm an idiot.

First of all there are three Autosize options of interest here: "4:3", "DVD" and "DVD 16:9". (Read: there's no "DVD 4:3").

Let's take the questions/notes one step at a time:

1. I've got a 4:3 TV. Considering I don't want to lose any part of the picture in the conversion, which ratio should I go for? 4:3, DVD, or DVD 16:9?

2. If I have a e.g. 640x272 video and convert it without checking the letterbox option or calculating the letterbox fields in the Filters tab, what will happen with the empty space?

3. ffmpegX is giving me a target file with a resolution whose width is larger than 640. I have to calculate whether black bars are needed right? And to do so, I have to solve the following equation (Y3 is the unknown number): Y1xY2 (original source) = 640xY3. Then if Y3 is smaller than 480 black bars need to be added. If I choose the letterbox option (next to QT decoding), the black bars will be added automaticaly. If I want to mess with the letterbox fields in the "Filters" tab, do I enter the black bar values that correspond to the 640xY3 case? If we're talking absolute values here, these would be different to the ones that correspond to Y1xY2.

4. 720x576, which is the resolution of the target file ffmpegX is giving me in example #1 in my post, means a ratio of "1.25:1".
A. This is neither 16:9 (1.77:1), nor 4:3 (1.33:1) -- what's going on here?
B. 720x576 -> 640x512. What's going on with black bars now?

Seriously, this feels like rocket science.

[Case]

1. I've got a 4:3 TV. Considering I don't want to lose any part of the picture in the conversion, which ratio should I go for? 4:3, DVD, or DVD 16:9?

The '4:3' setting should not be used for converting to DVD.
The 'DVD' setting is for 4:3 full frame. It could as well be named 'DVD 4:3'.
The 'DVD 16:9' setting is for widescreen frames. That's okay for 4:3 tv set owners, as any standalone DVD player can auto-letterbox a 16:9 picture to a 4:3 screen (or pan-and-scan, if you so prefer, argh!)
The benefit of making 16:9 DVDs wherever possible, is using the vertical resolution to the max. Read up on 'anamorphic' to learn the gory details. (There used to be an excellent Flash file that explained anamorphic, but it seems gone now. )

2. If I have a e.g. 640x272 video and convert it without checking the letterbox option or calculating the letterbox fields in the Filters tab, what will happen with the empty space?

If your target format is DVD, then the output will be a stretched picture, no empty space, just distorted to fill full screen without any regard for the original aspect ratio.

4. 720x576, which is the resolution of the target file ffmpegX is giving me in example #1 in my post, means a ratio of "1.25:1".
A. This is neither 16:9 (1.77:1), nor 4:3 (1.33:1) -- what's going on here?

Your calculation would be correct for square pixel movies, but it's different for rectangular pixel video. Think of it like an added parameter to the video, describing the aspect ratio for playback, regardless of the framesize. A little 'stretching' of the frame will make it either 16:9 or 4:3.

B. 720x576 -> 640x512. What's going on with black bars now?

Where does the 640x512 come from?

[Case]

3.

I think it's easier to use math like this:
The aspect ratio of your target movie devided by the aspect ratio of your source movie will give you the part that will fit between the letterbox bars. E.g. 1.78/1.91=0.93. So 93% of the height is picture, the remaining 7% is black: 3.5% on top, 3.5% on the bottom. 3.5% of the DVD PAL video height is 0.035*576=20 pixels.
This way, you don't need to bother with scaling or pixel aspect ratios in your calculation.

[konstantinos]

At the risk of sounding tiring, thanks again for continuing to answer my questions, I really appreciate it Case.

The inevitable follow-up...

RE: 1: So... which one should I go for? DVD or DVD 16:9?

RE: 2: Got that one, OK!

RE: 3: Uh...huh. A bit difficult but got it as well.

RE: 4A: "A little 'stretching' of the frame will make it either 16:9 or 4:3."

What will happen on my 4:3 TV? Will it be stretched to 4:3 or to 16:9 (black bars)?

RE: 4B: "Where does the 640x512 come from?"

OK, we've got 720x576. Following rumplestiltskin's method of calcuation we have:

640/720*576=512 (which is a multiple of 16)

So we're ending up with a 640x512 target file? Isn't 480 the max? What happens with black bars now?

I've got another question, but I'll hold it until this is cleared first.

As always, thank you very much for your help!

[Case]

RE: 1: So... which one should I go for? DVD or DVD 16:9?

For a 4:3 tv, the results are the same. But for a computer monitor or a friend's widescreen tv (or your future tv), it does make a difference. Encoding for widescreen means less letterbox black, thus more detail in the picture. I would only use DVD 4:3 for a ~4:3 source file.

RE: 3: Uh...huh. A bit difficult but got it as well.

That's what makes a simple checkbox that automates everything so appealing.

RE: 4A: "A little 'stretching' of the frame will make it either 16:9 or 4:3."
What will happen on my 4:3 TV? Will it be stretched to 4:3 or to 16:9 (black bars)?

If you set your standalone DVD player to "Video>TV screen>4:3 Letterbox", then the player will display 720x576 with a 4:3 flag to full screen, and it will display 720x576 with a 16:9 flag to a 16:9 area within the 4:3 screen by adding (extra) letterbox bars. (A 2.35:1 movie would have letterbox bars encoded into the 16:9 video, and the DVD player could add extra bars to make it 4:3. This is how many commercial DVDs work, too.)

RE: 4B: "Where does the 640x512 come from?"
OK, we've got 720x576. Following rumplestiltskin's method of calcuation we have:
640/720*576=512 (which is a multiple of 16)
So we're ending up with a 640x512 target file? Isn't 480 the max? What happens with black bars now?

Seeing a resolution of 720x576, I would assume it was taken from (or made for) a tv-like source (DVD, DV), having an aspect ratio of either 4:3 or 16:9. If you would convert that to 640xsomething, then I would assume its target format (AVI, MP4) wouldn't need letterboxing in the conversion process.
(640/16)*9=360 or (640/4)*3=480.

[konstantinos]

Future generations will be saying stories about your courage, putting up with all of my questions.

RE: 1: Excellent, I finally got it. DVD 16:9 (for future-proofness), unless the original source is 4:3 in which case it's best to go with DVD. (Correct me if I'm wrong.)

RE: 3: You're referring to the "Letterbox" option next to the "Decode with QT" one, right?

Also: will having this option checked at all times cause blackbars to appear even when they're not needed? (e.g. in a 4:3 to 4:3 conversion, or something) In other words, can I leave it checked at all times?

RE: 4A: "If you set your standalone DVD player to "Video>TV screen>4:3 Letterbox", then the player will display 720x576 with a 4:3 flag to full screen, and it will display 720x576 with a 16:9 flag to a 16:9 area within the 4:3 screen by adding (extra) letterbox bars. (A 2.35:1 movie would have letterbox bars encoded into the 16:9 video, and the DVD player could add extra bars to make it 4:3. This is how many commercial DVDs work, too.) "

1. I won't be losing part of the picture/frame in none of the two cases (4:3 and 16:9) -- is that correct?

2. Where did that 2.35:1 ratio come up? (720x576 is 1.25:1, isn't it?)

==

Final question (I know, unbelievable, but it's a 5-fold question so I guess it's not too much of a surprise): to convert an AVI to DVD (ffmpeg) for reproduction on my 4:3 TV, I do the following:

1. Select DVD (ffmpeg) as the target format.
2. In the Video tab, set Autosize to DVD 16:9.
3. In the Options tab, I check the "Decode with QT" and "Letterbox" options.
4. I'm done.

1. Is this correct?
2. Can I apply this to any source file regardless of its resolution (unless it's 4:3, in which case I'll go for DVD 4:3)?
3. Can I disregard rumplestiltskin's method of calculation?
4. Since you talked about rectangular pixels, etc. I shouldn't be bothered that most of the times the width or the height of the target file is bigger than 640 or 480 respectively -- correct?
5. One of my tests goes from 624x352 (source) to 720x480 (target)? Should it bother me that the target resolution is bigger than the source one? (I'm thinking audio files here, where going from a low bitrate to a higher one isn't possible. Programs may do it but it's pointless.)

As always, thank you!

[Case]

1. Correct.
3. Correct.

Also: will having this option checked at all times cause blackbars to appear even when they're not needed? (e.g. in a 4:3 to 4:3 conversion, or something) In other words, can I leave it checked at all times?

If the program determines that zero pixels of letterbox are needed, then you'll get just that: no bars.
There are exceptions to every rule, that's why it can be unchecked. But for most conversions to DVD you can leave it checked.

4A 1. Correct.
4A 2. I made that number up (well, sort of; it's a common a.r.), to illustrate the double letterboxing, once in the conversion and once by the player.

5 1. You could make more tweaks if you'd like, but the result would be good, most of the times.
5 2. Yes.
5 3. Never disregard our friend rumplestiltskin's good advice. There is more than one way that lead to good results.
5 4. 640 wide is not valid for DVD. The video size that gets filled in by the Autosize menu is valid.
5 5. Upscaling doesn't make the video better, but DVD supports only a few resolutions, so, whenever possible, you pick the one that's doesn't involve downscaling, if you want a quality output.

[konstantinos]

5 3. Never disregard our friend rumplestiltskin's good advice. There is more than one way that lead to good results.

I didn't mean that rumplestiltskin didn't know what he was saying... I just asked if I could skip the calculations as he suggests (a bit time-consuming) and just go with the autosize method I described in my previous post? Is this OK?

5 5. Upscaling doesn't make the video better, but DVD supports only a few resolutions, so, whenever possible, you pick the one that's doesn't involve downscaling, if you want a quality output.

A-ha. So if I'm reading this correctly, you're saying that "just as long as you avoid lower resolutions, you're good to go" (read: "higher resolutions in the target file don't hurt"). Correct?

(This is the last follow-up!)

[rumplestiltskin]

No offense taken.

[Case]

Yes. Yes. Start converting already!

[konstantinos]

Excellent

rumplestiltskin, nice!

Case, you're a video-conversion guru and a hero for answering all of my questions!

Once again, thank you very very much for your help -- I really appreciate it.

[konstantinos]

Instead of creating a new thread, and since:

1. most of my line of thinking is detailed here
2. it's a quick question

...I thought it would be best to post here.

In case we want to use the "DVD mpeg2enc preset" (so that we can set 3:2 for NTSC FILM), do we proceed with the following selections?

1. In "Video >> Autosize" we choose "DVD 16:9" (unless the original is 4:3).
2. In "Options >> mpeg2enc" options we choose "Set 3:2", "Decode with mplayer" (since we want subtitles support), "Letterbox" (I don't remember why we do that...) and de-select "Decode with Quicktime" (since we're going mplayer).
3. In "Options >> Profile" we choose "DVD".

Are all of the above correct?

Thanks in advance for your help!