[mythtv] new feature saving the ring buffer

[Louie Ilievski]

On Monday 29 August 2005 01:40 pm, Marcelo Toledo wrote:
> I am looking forward in implementing a new feature that will save the
> ring buffer. What it will do: While watching live tv you might save what
> has past and still in the ringbuffer, so you will press a key
> combination and it will store what have been recorded as a recorded show
> with the name "Live TV date hour".
>
> This is not an easy task and we have a few problems, including:
>
> 1. The file header is missing
> 2. The ring buffer can loop
>
> I would like to hear possible problems and suggestions of how can I fix
> them.
>
I have put some thought into this as well, thinking that maybe some day I 
could try to implement this feature.  A couple of problems that came up:

1) In some circumstances, you could have been in Live TV mode for quite a 
while, with a very large ring buffer set up.  Therefore, when you DO decide 
to record a show that maybe just came on, what do you do with all of the junk 
before that?  Do we use some tool or write our own code to cut off all of the 
preceding junk (this brings us back to the thoroughly discussed MPEG cutting 
issue)?  Do we just store it all and just put a bookmark at the beginning of 
the show intended to be recorded by using the program guide data?

Obviously the second option isn't that practical.  It would be a very large 
waste of disk space.  On the other hand, cutting the previous junk off seems 
like it might be feasible.  I forget all of the issues with the MPEG2 
cutting, but I know one concern in the past is that it's not frame accurate.  
In this case, this is acceptable.  Cutting on GOPs is plenty accurate.  And 
since we're only making one cut at the beginning, MAYBE there wouldn't be any 
a/v sync issues??  I'm not sure how we would go about achieveing this task.  
I believe I've learned a few things over time about the devs and their 
policies regarding this project and I think one of them is that there will be 
no external dependencies if it can be helped (which makes sense).

2)  This one is not as much of a problem, but it still came to mind.  Our 
LiveTV profile is often quite different then our Default recording profile as 
far as bitrate goes.  How do we resolve this?  Just store this show at the 
higher bitrate?  Maybe schedule a transcode or something?  I'm sure there are 
many options for this one, but I thought I'd throw it out there.

In regard to aaron's post about the overhead of copying the buffer and such, I 
don't think this is an issue.  I think it would be best to just continue 
recording as is and then copy the program over after it is finished.  I saw a 
friend's TiVo quite a while ago and I think it does something like this 
because I remember sitting there staring at a "Please Wait" message.  Now, I 
can't remember if this was right when he decided to start recording or after 
it stopped, but either way I think that issue can be fairly easily resolved.

~Lou
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