Customizing DVD title playback:
Background:
Playing sections of titles in non-original order, or stringing separate titles together can take several forms. At the heart of it are cells: time intervals stored in the instructions to DVD players. Every video has at least one of these intervals that are written by DVD authoring software, and the video itself is unaffected and un-altered. Chapters & Programs may be assigned to individual cells, and they have an individual ID based on their VOB; i.e. VOB 1 may have cells 1 – X, as will VOB 2, 3 etc.
Much simplified, a DVD is a set of instructions on which cells to play, in what order, according to a somewhat lengthy set of rules. These directions can be included in a rather straightforward way in the instructions for the player, or they can be the result of a limited scripting capability included in the DVD spec. Generally scripting takes longer, both to write and for the player to execute, but it is safer when it comes to obeying all the rules.
DVDA 4 uses a lot of scripting, shielding the author/developer from having to worry about which rules apply, where, but sacrifices a bit of speed &/or simplicity doing so. One option is to render your DVD layout to your hard drive using DVDA, then modifying that layout using PgcEdit or other, similar software – I’ll explore a couple of these alternatives later.
DVDA 4:
One popular way of stringing titles together is the playlist; in DVDA 4 a series of scripts are created that channel playback through otherwise individual titles in the order you set. One downside is that because it relies on scripts, the pause may be greater between titles; if the titles are not located consecutively on the disc, there will also be a delay as the laser moves across the disc, and there is some delay introduced as a new title is first read by the player. On the other hand audio sync problems are lessened, because any audio in an individual title is self-contained, and space is saved on the disc itself because repeated assets only have to appear on the disc once.
A compilation allows you to string separate video together in whatever order you like, but this suffers from not being able to add chapters, besides those that DVDA 4 inserts at the start of every individual video on the track. A video compilation also suffers because video appearing in more than one comp is written more than once to disc.
What are generically referred to as Angles provide other methods of ordering playback. DVDA 4 lets you create interwoven angles: this is an alternative video track or tracks that continue to use the original audio. If the new video was located too far from the audio track [that wedded to the original video], playback would really suffer from the player’s laser constantly jumping back and forth – for this reason the new and old videos are interwoven [a short section of one followed by a short section of the other] to keep them physically close together on the disc. To accomplish this DVDA 4 [as well as other DVD authoring programs] has to do the final encoding, which might cause problems or added work because in DVDA 4 encoder settings are very limited, i.e. you cannot set the field order etc…
You’ll also read about stories, seamless branching, & pseudo-seamless branching… On a retail DVD you might see 2 separate titles, both referring to the same video, but each listing different cells and cell orders. The DVD’s instructions may point inaccurately to these cells, and you might see different VOB numbers or IDs associated with cells of the same video title. You can come close to this using PgcEdit on DVD layouts produced in DVDA 4, though I can’t test compatibility on every player [mileage may vary].
Faking (?) Branching:
To accomplish this first create and encode your video title including all content [everything for 2 versions for example]. [Thanks to George for this method:] Import this video twice to a menu page – importing it to root [at the same level as the menu] will not work. Make sure chapter points are at least set where you want your video playback to differ – DVDA will only create a new cell where you place a chapter. Limit the playback time of your second instance or copy – if your second title version includes chapters 1 – 5, but not 6, limit playback to chapters 1 – 5. Finish creating your DVD layout and prepare to your hard drive – optionally you might want to store a copy in another folder for backup.
Opening this rendered layout in PgcEdit, locate your titles in the leftmost column. Select your second title, and click the button [or right click the title] for Edit PGC. At the bottom of the window that opens, click the button to add a cell, selecting the next chapter or cell you want to play, optionally letting PgcEdit create a matching chapter/PTT number. Besides clicking OK a time or two and saving your modification, that’s about it. Your second title will play in the order you set, & hopefully the Next button will work as expected. Because you’re not relying on scripting between every cell, the transition should happen noticeably quicker.
Setting chapter menus can be a hassle of course, but you couldn’t even hope to set them with a play list; every cell does not need a chapter, and you can preserve [reuse] common cells with chapters. [It’s a bit more work, but in the same Edit PGC window you can remove a chapter number from a cell.] You can set a variable for either title adding scripts or duplicating menu pages so scene menus work.
There are loads of possibilities really, but the downside of potential audio sync problems remains... Audio and video clocks and/or time measurement are simply and basically different. A cell may start at a clean break in the video stream, but not necessarily at a break in the audio. When they jump chapters it’s not a big deal because the viewer is expecting discontinuity. I’ve read that this is the reason behind branching not being more widely supported in DVD authoring software – that’s not to say that if it’s a problem you can’t potentially cure it through careful audio design and editing.
You might also find a cure for some design problems using cell commands… I haven’t seen them used that often [which really might not mean much – if anything], but to use them dive back into PgcEdit, opening your DVDA created DVD layout. Select your title on the left column, select the cell commands line on the right. Click the button for Add After, and you’ll see a line with NOP appear. Select that new line, right click and select edit cmd. Make your choices in the menu window that pops up. Now go back to your title, and Edit PGC. In this edit window there’s a box in each cell row for Cell Cmd # -- type in the number for the cell command you just entered [this number appears at the far left of the command in the main PgcEdit window].
Happy Authoring!
Background:
Playing sections of titles in non-original order, or stringing separate titles together can take several forms. At the heart of it are cells: time intervals stored in the instructions to DVD players. Every video has at least one of these intervals that are written by DVD authoring software, and the video itself is unaffected and un-altered. Chapters & Programs may be assigned to individual cells, and they have an individual ID based on their VOB; i.e. VOB 1 may have cells 1 – X, as will VOB 2, 3 etc.
Much simplified, a DVD is a set of instructions on which cells to play, in what order, according to a somewhat lengthy set of rules. These directions can be included in a rather straightforward way in the instructions for the player, or they can be the result of a limited scripting capability included in the DVD spec. Generally scripting takes longer, both to write and for the player to execute, but it is safer when it comes to obeying all the rules.
DVDA 4 uses a lot of scripting, shielding the author/developer from having to worry about which rules apply, where, but sacrifices a bit of speed &/or simplicity doing so. One option is to render your DVD layout to your hard drive using DVDA, then modifying that layout using PgcEdit or other, similar software – I’ll explore a couple of these alternatives later.
DVDA 4:
One popular way of stringing titles together is the playlist; in DVDA 4 a series of scripts are created that channel playback through otherwise individual titles in the order you set. One downside is that because it relies on scripts, the pause may be greater between titles; if the titles are not located consecutively on the disc, there will also be a delay as the laser moves across the disc, and there is some delay introduced as a new title is first read by the player. On the other hand audio sync problems are lessened, because any audio in an individual title is self-contained, and space is saved on the disc itself because repeated assets only have to appear on the disc once.
A compilation allows you to string separate video together in whatever order you like, but this suffers from not being able to add chapters, besides those that DVDA 4 inserts at the start of every individual video on the track. A video compilation also suffers because video appearing in more than one comp is written more than once to disc.
What are generically referred to as Angles provide other methods of ordering playback. DVDA 4 lets you create interwoven angles: this is an alternative video track or tracks that continue to use the original audio. If the new video was located too far from the audio track [that wedded to the original video], playback would really suffer from the player’s laser constantly jumping back and forth – for this reason the new and old videos are interwoven [a short section of one followed by a short section of the other] to keep them physically close together on the disc. To accomplish this DVDA 4 [as well as other DVD authoring programs] has to do the final encoding, which might cause problems or added work because in DVDA 4 encoder settings are very limited, i.e. you cannot set the field order etc…
You’ll also read about stories, seamless branching, & pseudo-seamless branching… On a retail DVD you might see 2 separate titles, both referring to the same video, but each listing different cells and cell orders. The DVD’s instructions may point inaccurately to these cells, and you might see different VOB numbers or IDs associated with cells of the same video title. You can come close to this using PgcEdit on DVD layouts produced in DVDA 4, though I can’t test compatibility on every player [mileage may vary].
Faking (?) Branching:
To accomplish this first create and encode your video title including all content [everything for 2 versions for example]. [Thanks to George for this method:] Import this video twice to a menu page – importing it to root [at the same level as the menu] will not work. Make sure chapter points are at least set where you want your video playback to differ – DVDA will only create a new cell where you place a chapter. Limit the playback time of your second instance or copy – if your second title version includes chapters 1 – 5, but not 6, limit playback to chapters 1 – 5. Finish creating your DVD layout and prepare to your hard drive – optionally you might want to store a copy in another folder for backup.
Opening this rendered layout in PgcEdit, locate your titles in the leftmost column. Select your second title, and click the button [or right click the title] for Edit PGC. At the bottom of the window that opens, click the button to add a cell, selecting the next chapter or cell you want to play, optionally letting PgcEdit create a matching chapter/PTT number. Besides clicking OK a time or two and saving your modification, that’s about it. Your second title will play in the order you set, & hopefully the Next button will work as expected. Because you’re not relying on scripting between every cell, the transition should happen noticeably quicker.
Setting chapter menus can be a hassle of course, but you couldn’t even hope to set them with a play list; every cell does not need a chapter, and you can preserve [reuse] common cells with chapters. [It’s a bit more work, but in the same Edit PGC window you can remove a chapter number from a cell.] You can set a variable for either title adding scripts or duplicating menu pages so scene menus work.
There are loads of possibilities really, but the downside of potential audio sync problems remains... Audio and video clocks and/or time measurement are simply and basically different. A cell may start at a clean break in the video stream, but not necessarily at a break in the audio. When they jump chapters it’s not a big deal because the viewer is expecting discontinuity. I’ve read that this is the reason behind branching not being more widely supported in DVD authoring software – that’s not to say that if it’s a problem you can’t potentially cure it through careful audio design and editing.
You might also find a cure for some design problems using cell commands… I haven’t seen them used that often [which really might not mean much – if anything], but to use them dive back into PgcEdit, opening your DVDA created DVD layout. Select your title on the left column, select the cell commands line on the right. Click the button for Add After, and you’ll see a line with NOP appear. Select that new line, right click and select edit cmd. Make your choices in the menu window that pops up. Now go back to your title, and Edit PGC. In this edit window there’s a box in each cell row for Cell Cmd # -- type in the number for the cell command you just entered [this number appears at the far left of the command in the main PgcEdit window].
Happy Authoring!