[mythtv] Record now?

[Bruce Markey]

Chuck Wolber wrote:
> 
>>I guess the feasibility of this depends on how the ringbuffer works -
>>can you tell just by examining the ringbuffer file where you started
>>watching a particular channel?  If you were surfing and stumbled on
>>"Friends" and decided to tape it, you only want to copy the portion of
>>the ringbuffer that is "Friends".
> 
> 
> TiVo starts from where the program started. It can tell this simply by 
> the time and which program it senses that you are currently watching.

That's an interesting way to think of it but, of course, TiVo
has no way to sense what the viewer is doing. It does, however,
know what channel it is tuned to and when the ringbuffer was
restarted. If you choose to record the current show, you are
given the choice of continuing to record at "Best" quality
saving the previous portion or to change quality starting
from the current time.

To continue at "Best", it appears it is simply renaming the
ringbuffer to the filename for the show. This works because
the open filehandle is unaffected by the fact that the inode
number is associated with a different directory entry. In
Unix, you can open any file for writing, rename it, and
continue to write (but you cannot move it to another
partition and continue writing to it unless you reopen ;-).

So, if you change channel at 7:05 then decide at 7:10 to
record this half hour show, the result is 7:05-7:30. However,
this gives unexpected results if you were on the channel
before the show started. If you changed channel at 6:55 then
choose to record at 7:10, the result is 6:55-7:30 (try it ;-).

MythTV could do the same rename trick if there is nothing
special about the ringbuffer file format. However, cropping
a ringbuffer that started before the show's start time is
trickier.

>>If you change channels, does the ringbuffer start over from the begining
>>of the file?  If not, does it indicate that a channel change occured or
>>does it just basically have a capture of what I've been watching (and,
>>gosh, what are the privacy implications of that!:-)
> 
> 
> Again, TiVo kills the ring buffer and starts over when you change 
> channels. In fact it kills the ring buffer a little too easily if you ask 
> me. I've lost more than a few programs I was intending to record.

My first experience with a digital recorder was the ATI AIW
windoze software. You set the ringbuffer size (say, two or
three hours) and you could move back and forth to previous
shows on previous channels. This made perfect sense to me.
When I got a TiVo, I was shocked that it restarted the
buffer when you change channel (doh! =). I believe they only
do this for the sake of the record in progress feature starting
from the channel change without having to crop the buffer.

--  bjm