The 1st step is gathering together your video & any images you want to use -- it doesn't hurt to sketch out a map, as rough or detailed as you like, so you have a flow chart to guide or remind you of what content you'll use & how it will be inter-connected.
Next, you want to get all that content you gathered into the proper format for your project. For a DVD that means DVD-spec mpg2 in one of several, "spec-legal" sizes, usually but not always 720 x 480 or 576 -- for a Blu-Ray that means Blu-Ray spec AVC/H.264, VC1, or mpg2, & again you have several size options, though the most common is 1920 x 1080. Blu-Ray video is usually 24 fps [23.976], while DVD video may be 29.976 fps [NTSC], 25 fps [PAL], or 23.976 [24 fps] with pulldown added [pulldown = flags telling the player which frames to repeat to achieve the target fps] -- if the source is 24 fps [23.976], adding physical frames to reach the target fps makes the file larger than using pulldown, so you have to use more compression to make the video fit on a DVD, meaning lower quality. The more compression used [i.e. the lower the bit rate], the smaller the file(s) will be, but that also equals lower quality. Watch Out: older TVs had a limited dynamic range -- couldn't display the blackest black or whitest white -- & software as well as players may make that adjustment for you, either expanding or contracting the color range or palette used... Unless you were preparing something for broadcast, compressing the color range hasn't been a *Must Do* for several years [it's part of broadcast legal specs], but one or more apps/processes can change it for you behind the scenes, sometimes leading to unexpected, usually poor results -- if you're aware it can happen you know to watch for it.
DVD menu background images or video may be 16:9, 4:3, or have the same backgrounds in both aspect ratios -- when you have both, which one's shown depends on the player settings or via menu settings included in the DVD. Blu-Ray backgrounds are usually 1080p [1920 x 1080]. Retail Blu-Ray movies normally use Java-based menus, but the software used for those retail discs costs many thousands of dollars -- otherwise menus are created the same way as DVDs, in the same software. Graphics for Button Highlights -- the parts of a menu that change colors or glows etc. when selected -- can be created at the same time you're creating your menu backgrounds. While there are tricks to use & show a still image, most of the time everything you see on a DVD or Blu-Ray you create will be video -- encoding menu video beforehand, just like encoding your main video beforehand, hopefully will allow you to skip the normally limited, relatively poor encoder built into most DVD/Blu-Ray authoring apps. If not, make sure stuff like your menu backgrounds is higher quality than necessary, ideally stored in a lossless format, so re-encoding won't hurt so much.
Audio is handled separately, & is normally AC3 stereo &/or 5.1 -- most people don't have setups [hardware or software] to listen to 6 channel audio, so if you only use one track having it stereo is safer. That said, the 5.1 to stereo converters built into many players can make dialog clearer than just playing an equivalent stereo AC3 track. The choice to include one or the other or both is often heavily influenced by how much space is available -- on a single layer disc any space you don't use can be devoted to larger, higher quality video files. If you choose to do it, fake 5.1 audio can be generated from stereo audio files, which can sometimes sound noticeably better. Other audio formats are rare for a reason -- .wav is too large, DTS software too expensive, & mp3 too low quality.
Subtitles can be in 2 forms, as regular text or as graphics images on transparent backgrounds, the latter being how they're stored on a DVD/Blu-Ray disc -- DVD/Blu-Ray authoring software may deal with one or the other, so you may for example have to create subs in transcriptioning software [or strip the text from a recorded video etc.], convert that text to graphics-based subs, & then import it into your authoring app.
Once your content's ready the next step is bringing it into your authoring app where you set up what happens & when. Everything is triggered by something else -- you're mostly concerned with what happens when something's selected, when the viewer presses a button on the remote, & when a video [including as a menu background] is done playing -- but 1st you set any chapters for your video(s) so you can [optionally] target those with your buttons as well. Chapters [& the cells they're based on] can only occur at I frames [frames containing a complete image] -- because of that & varying player performance you're best off placing/creating your chapters 15-25 frames [or more] into a scene. If you're creating a dual layer DVD, you'll need one chapter/cell near the middle that can be used for the layer break. Once you have your chapters set most authoring apps can create chapter menus if you wish, & then you can get down to the business of adding/creating menu pages, placing your menu buttons, & tying everything together.
The average pro or retail DVD will have a brief intro video than segues or morphs into the looping main menu background -- a chapter/cell is placed at that point & that's when any buttons become operative. It's common not to actually loop that menu however, instead having the end of the menu video trigger a copy of that menu minus the intro, & that copy does loop... this is because having the intro & menu video combined makes for smoother play, without a pause when the menu actually starts, but that also causes more of a delay when the menu video loops. Buttons are usually set on that main menu [& copy] that take the viewer to setup menus, e.g. for audio, a special feature menu(s), chapter menus, & of course play any movies. However, it's very common to have those menu buttons point to a short transition video that in turn triggers the menu or video target once it's done playing -- just like the joined Intro/Main menu video, secondary menus can contain a transition video that ends in the menu video, triggering a looping copy of that menu once it's done playing. Trying hard not to get *too much more* complicated, I'll just note that in practice menus with hidden buttons are also often used just to play a short video as their background -- it can be smoother since they're located physically close to other menus on the disc -- while completely hidden [invisible] menus are often used as places to park scripting. In what may by now be a hopeful, last note if your brain's starting to numb, I think the time of really complex DVDs has peaked, with the trend being towards less is more.
