Friday, December 10, 2010
Sunday, December 5, 2010
Loopy DVD Menu Videos
My first DVD using Sony's DVD Architect has a video background for the menus. Being reckless I started creating the video for the menu before learning anything about DVD Architect (DA). I had my video fade up from black at the start and fade down to black at the end. In DA I added the video as the background media then previewed it. The video played and as I anticipated it looped back to the beginning and started again. Seeing this I had an epiphany; if I added a final transition at the end so that the last frame of the video was identical to the first frame at the beginning of the video it would appear as if the menu video was an endless loop. This was quickly followed up with another thought, "Video loops just like every professional DVD menu - doh!" I went back and re-edited and re-rendered my video for looping. In the DA preview I noticed a choppy gap as the video looped but convinced myself it was just an artifact of the preview, the final DVD would be fine.
Later when I watched the actual DVD I saw the choppy transition still existed. At that point I had been working on the DVD and its contents for months and my interest in solving (if it was even possible) a minor issue was very low.
Then recently I happened to be watching the main menu on the documentary "Good Hair" and noticed that when it reached the end of the video there was a brief transition to what appeared to be a different resolution still image of the main menu, then the video started playing again. That got me thinking about the loop transition on my DVD. It turns out that the main reason the loop was choppy was because the length of the menu video was calculated incorrectly.
On the Menu Page Properties under General is an entry for Menu length, the default value is Auto calculate and the length it has calculated is in the read only entry Length just below.
The Menu Page Properties with Auto calculate selected.
In the case of my video the calculated length was about 0.2 second longer than the actual video and this seemed to cause problems during playback. The solution was to set the actual length of the video manually. The actual length of the video can be found in the lower right of the Timeline pane, however the length is shown in seconds and frames. This not entirely helpful because the time to be entered in Length must be in minutes, seconds, and milliseconds. To get the time make sure that the media timeline pane is showing; from the menu select View - Timeline. In the time bar above the video right-click and select Time and Frames.
Changing the display to Time and Frames in the Timeline.
Zoom in on the timeline so that a hash mark appears for each frame, now click to place the cursor at the last frame you want to show which is probably the last frame. Now right click the timeline bar again and select Time. The length of the video is shown on the left side of the pane right above the video.
Set the display to Time and the actual video length is shown.
Return to the menu properties and click on Auto calculate and a list appears; choose Specify. Now the video time determined above should be copied to the Length value.
Specify the actual video length.
Preview the menu and you should find that it loops seamlessly from the end of the video back to the beginning. I don't understand why the estimated length doesn't match the actual length, guesses include: slight discrepancies between the audio and the video (i.e. the audio track is longer), the data used to calculate the length is bad or the calculation formula is wrong. In any case it seems easy enough to correct to create professional looking menus with video backgrounds. I learned a few other interesting possibilities during this exercise. One is that the loop point defines the beginning of the loop, this is how some menu videos have an introductory part that is only shown once along with a location to start loop playback so that there is a seamless loop. Another possibility is that when navigating from menu to menu a "transition video" can be inserted between them. When a viewer selects a button, instead of navigating immediately to the next menu the link connects to a video that has been placed at the root of the DVD file structure. The End Action of the transition video then links to the menu to be displayed. This is a fairly common technique I have seen on several of the more highly produced DVDs.
The Menu Page Properties with Auto calculate selected.
In the case of my video the calculated length was about 0.2 second longer than the actual video and this seemed to cause problems during playback. The solution was to set the actual length of the video manually. The actual length of the video can be found in the lower right of the Timeline pane, however the length is shown in seconds and frames. This not entirely helpful because the time to be entered in Length must be in minutes, seconds, and milliseconds. To get the time make sure that the media timeline pane is showing; from the menu select View - Timeline. In the time bar above the video right-click and select Time and Frames.
Changing the display to Time and Frames in the Timeline.
Zoom in on the timeline so that a hash mark appears for each frame, now click to place the cursor at the last frame you want to show which is probably the last frame. Now right click the timeline bar again and select Time. The length of the video is shown on the left side of the pane right above the video.
Set the display to Time and the actual video length is shown.
Return to the menu properties and click on Auto calculate and a list appears; choose Specify. Now the video time determined above should be copied to the Length value.
Specify the actual video length.
Preview the menu and you should find that it loops seamlessly from the end of the video back to the beginning. I don't understand why the estimated length doesn't match the actual length, guesses include: slight discrepancies between the audio and the video (i.e. the audio track is longer), the data used to calculate the length is bad or the calculation formula is wrong. In any case it seems easy enough to correct to create professional looking menus with video backgrounds. I learned a few other interesting possibilities during this exercise. One is that the loop point defines the beginning of the loop, this is how some menu videos have an introductory part that is only shown once along with a location to start loop playback so that there is a seamless loop. Another possibility is that when navigating from menu to menu a "transition video" can be inserted between them. When a viewer selects a button, instead of navigating immediately to the next menu the link connects to a video that has been placed at the root of the DVD file structure. The End Action of the transition video then links to the menu to be displayed. This is a fairly common technique I have seen on several of the more highly produced DVDs.
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