[mythtvnz] Cutting H.264 DVB-T files with ffmpeg without transcoding

[David Moore]

David Moore wrote:
> Hi folks. I have posted a very raw version of a script called mythcutnz 
> at git://gist.github.com/490296.git or http://gist.github.com/490296. If 
> you want to try it I suggest you use recordings you don't mind losing or 
> back up the recording before you run the script. You'll still have 
> issues with the seek table if you go back to a backup but that can be 
> fixed with mythtranscode and some sql.
> 
> Please read the help/usage text before you try it.
> 
> As Jeremy Clarkson says "how hard can it be"? Well harder than I 
> initially thought because:
> 
> - Frames to time conversion needs either divide by 25 or divide by 50 
> depending on channel. Not a lot of testing so far but I'm using the 
> "tbc" parameter reported by ffmpeg to work this out. Might not work on 
> all channels.
> 
> - Mythcommflag has never worked well for me and threw a bunch of 
> database errors when I tested it so I used mythtranscode for rebuilding 
> the seek table. However it (or the ffmpeg code it uses) seems to double 
> the real frame numbers. There seems to be a connection between the seek 
> table and myth's timeline when playing/editing a recording. This caused 
> weirdness like the recording magically doubling in length. Fixed (maybe) 
> by updating the frame numbers with sql.
> 
> - &%#$! vlc threw a spurious error about a missing codec when actually 
> it was a missing codec parameter.
> 
> For speedy testing use a recording with an AC3 audio track (only TV3 
> AFAIK) otherwise the whole recording has to be transcoded with vlc 
> before cutting starts. Or use a short recording without AC3 audio.
> 
> I haven't actually run the script as a user job yet. Just tested from 
> the command line. Probably needs a bit of sql to add to the myth job 
> queue before running as a user job.
> 

Update: I had another look at TS vs PS formats and I can possibly get 
this working better with TS and (possibly) produce better final files. 
My main objection to TS was seek problems but it looks like 
mythtranscode can fix this.