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Advanced options

Sometimes you need to do more than just convert subtitles to BDN XML format. You may also want to make them larger or smaller, make them display in a different position on the screen, or even change the colors. BDSup2Sub can do all these things.

The Conversion dialog

The Conversion Options dialog includes options for changing the size and speed of subtitles. Speed changes will allow you to keep subtitle timing correct when changing the framerate. If you prefer, you can also resize manually using the 'free scaling' option. Finally, you can adjust when the first subtitle appears or the minimum time a subtitle will appear on screen.

1. Convert Resolution

Use this option to resize subtitles for conversion to a different resolution. Only standard Blu-ray resolutions are supported. This will ensure that not only is the size changed, but also that the PAR1 is corrected to retain the correct shape.

2. Change frame rate

You can change the speed of the subtitles when you change framerates. Typically this is only necessary for PAL to NTSC or NTSC to PAL conversions2.

3. Force all

Forced subtitles are displayed regardless of whether you have selected them for playback or not. You can set or disable that here, but only for an entire subtitle stream3.

4. Apply free scaling

You can also resize subtitles manually using this option. This is primarily useful for changing the size of subtitles relative to the size of the picture. If you are resizing the videos and want the subtitles resized to match, use Convert resolution instead to make sure the PAR1 remains correct.

5. Subtitle delay and display length

These options allow you to change when the first subtitle appears and ensure each one is displayed long enough to be seen.

Delay (ms)

This is the delay between the start of the video and appearance of the first subtitle. It will not change the amount of time between subtitles4.

Fix too short frames

Each subtitle will be set to display for a particular period of time. If this is too short, it won't be on the screen long enough to be seen. You can adjust the minimum display time for a subtitle, in milliseconds, here5.


1 PAR, or Pixel Aspect Ratio, defines the ratio of width to height for a single pixel. The two most common HD resolutions, 1920x1080 & 1280x720 use square pixels, meaning the PAR is 1:1. Since they have the same shape (aspect ratio), but different resolutions, PAL and NTSC DVDs use different PARs and neither has square pixels.

2 For timing purposes, 25fps and 50fps can be considered PAL and 23.976fps, 24fps, 29.97fps & 59.94fps can all be considered NTSC.

3 In most cases forced subtitles on a DVD will be in their own stream, separate from regular subtitles in the same language, but that's not a requirement.

4 Each subtitle is a separate image which has its own timecode relative to the beginning of a title. The delay setting adds the same amount to each one.

5 1000ms is equivalent to 1 second. The default setting of 520ms means each subtitle will display for at least half a second.

Resize Filters

BDSup2Sub offers a number of different algorithms which can be used for resizing. You can choose the one you want from the Filter dropdown menu in the main window. The top image pane will show you the original subtitle and the bottom will show you the same subtitle resized with the selected filter. Below you can get an idea of the differences between different filters. Notice that some will blur the image, while others will sharpen it, but produce artifacts of one type or another. You should experiment with the different filters yourself to determine which one you prefer. You may even find that you prefer different filters for different subtitle files.

Repositioning subtitles

Subtitles may also be moved to a different position on the screen. Perhaps you want to move subtitles which overlap the movie, but you would like to move them so they only appear in the letterbox (black border) area. Or maybe you prefer your subtitles on the left or right, instead of the center of the picture. All of this, and much more, can be done by moving the subtitles6.

1. X position

X position refers to where the subtitle displays relative to the X axis. In other words, left to right. It can be moved to the left, right, or center. You may also specify an offset, which is particularly helpful if you are moving the subtitles to one side of the picture or the other.

2. Y position

Y position refers to where the subtitle displays on the Y axis. In other words, top to bottom. The options are just inside the picture (above the letterbox) or at the bottom of the frame. You may also specify an offset to move the subtitles up by a specific number of pixels.

3. Aspect ratio presets

These presets tell BDSup2Sub what part of the video frame is picture, and what part is letterbox. This affects both the preview in this dialog, as well as the placement of subtitles using the Y position inside bounds option. The presets are all targeted toward movies with a 2.35:1 aspect ratio7, which includes most theatrical releases. If your DVD title has a different aspect ratio, you should skp the presets, and set it manually (see #4).

4. Manual aspect ratio

For titles with an aspect ratio that doesn't match any of the presets, you can set it manually instead8. This will override any preset you may have already selected.


6 If you are trying to fit subtitles into a particular area, you may also need to resize in order to make them fit.

7 2.35:1 is really shorthand for an entire range of aspect ratios. Depending on the age of a movie, how it was actually filmed and edited, and even how it was transferred, encoded & authored to DVD, the actual aspect ratio could be anywhere from 2.33:1 (21:9) to 2.42:1. If you are trying to keep the subtitles out of the picture area, it may be necessary to leave some margin for error.

8 BDSup2Sub assumes the video is widescreen (16:9) and that the actual picture area is at least as wide. If your title is fullscreen (1.33:1 / 4:3) or simply narrower than 16:9 (1.66:1 for example) you should simply set this to 1.78 to indicate there is no letterbox.

Changing subtitle colors

Blu-ray subtitles use 16-bit color. That means more than 65,000 different colors are possible. However, only 15 of them may be used in a single subtitle stream. These colors make up the Palette. Separating it into image and colors this way allows you to change them en masse rather than being required to edit hundreds, if not thousands, of separate image files later. Some experimentation may be necessary to determine which numbers in a palette are actually used for what part of the subtitle images.

1. Choose Color

First find the color you want to change in the Choose Color dialog.

2. Change Color

The Change Color button will take you to another dialog where you can select the replacement color. The Preview area at the bottom of this dialog will give you and overview of what the new color looks like.

3. Save Palette

You can save your customized palette for use in future conversions using the Save Palette button.

4. Restore default colors

You can reset all colors in the palette to default values with the Restore default colors button.

5. Load Palette

You can apply a previously saved palette using the Load Palette button.


Table of Contents

  1. 1. Introduction
  2. 2. Advanced options
Written by: Rich Fiscus