On Wednesday in my post about the features coming to the Virgin Media TiVo I talked a bit about hard vs. soft padding. After some subsequent discussions I decided another post was in order to explain in a bit more detail. The concept of soft padding came up many years ago in the TiVo community, and by opposition the padding as it exists is therefore hard padding.
Hard Padding
Hard padding is what TiVo has today, and has had since padding was first introduced. When the padding is added to the recording it is ‘hard’ in that it is inflexible, and becomes part of the recording time, including conflict resolution. Let’s take the example from the previous post, where it is rumored that the new padding defaults in the UK will be 1 minute early and 4 minutes late. (I doubt that’s a coincidence with the fact clipping maxes out at 5 minutes.)
Say I had a three tuner box, as they do in the UK. And I want to record shows on channels 1, 2, and 3 from 8-9pm, and then a show on channel 4 from 9-10pm. Without any padding all three tuners would be used to record the shows on channels 1, 2, and 3 from 8:00:00 until 8:59:59. At 9:00:00 one of the tuners would change to channel 4 and immediately begin recording. How TiVo decides which tuner to use is unknown, but let’s presume tuner 1 for simplicity.
OK, now let’s add the padding. With start padding of 1 minute early and 4 minutes late now we have a problem. The first three recordings would run from 7:59:00 until 9:03:59, but the fourth would want to run from 8:59:00 until 10:03:59 – that’s a 5 minute overlap between two recordings. That brings conflict resolution into it. And clipping.
Let’s say clipping is on. If the first three shows were a higher priority than the fourth, you’d lose the first 4 minutes of the later show. That’s bad. If the later recording was a higher priority that any one of the first three then you’d lose the last minute of the earlier show. That’s worse.
If clipping is off then you have the same conflict, only now it is all or nothing. If the later show is a lower priority then it won’t record at all due to the conflict. And if it is a higher priority than any of the first three than the lowest of the three would get bumped.
Hard padding is just inflexible and you have to worry about conflicts, including any that come up later due to a schedule shift, etc. This is why most users won’t normally use padding. The downsides are just too great to use it regularly.
So what could solve this?
Soft Padding
The solution envisioned by the TiVo user community is soft padding. The idea of soft padding is that it is conditional. All of the conflict resolution and scheduling is done without consideration of the padding. The padding would be added after the To Do List is generated, and only if the tuner is free to allow the padding to be recorded.
Let’s take the above example again. Since the scheduling is done without consideration of padding the first three will be scheduled for 8:00:00 through 8:59:59 and the fourth for 9:00:00 through 9:59:59. There’s no conflict. Since the tuners are free before the first three recording they’ll actually all start at 7:59:00 for the 1 minute of soft padding. The two highest priority of the three will continue until 8:03:59 as two of the three tuners are free. The third will not be extended and will stop recording at 8:59:59, because the tuner is needed at 9:00:00 and so isn’t free to record padding.
Similarly the next recording will not start early, at 8:59:00, because the tuner is still in use. So it will start at 9:00:00. But it will run through 10:03:59 because there is a free tuner.
TiVo already prefers to use a different tuner for back-to-back recordings, so that would work well with soft padding. You can add some complexity to the logic to optimize it, but just adding soft padding to the existing scheduling and conflict resolution logic would be a huge leap forward. I know I’d use it on all of my recordings if it were available, and I’ve heard the same from many others over the years. If there were no harm in recording a few extra minutes on either end of a recording, no risk of causing a conflict, why wouldn’t you do it? It’d eliminate problems with shows that run just a few minutes, or even a few seconds, over their time slot.
This has been requested for years without it turning up. But I continue to think this would be a big improvement to the basic DVR functionality, and I don’t think there is a lot left that can be improved there. It hasn’t really changed in a long time, everything has been an add-on external to the core DVR features.
As for tacos, I like them both, but I tend to lean toward hard tacos for the crunch factor. 
