[mythtv-users] Finessing my recording edits

John Pilkington J.Pilk at tesco.net
Sun Oct 30 22:19:23 UTC 2011

On 30/10/11 16:33, Thomas Boehm wrote:
> Ian Evans wrote:
>> I've been editing down some of my recordings to save space. For the
>> most part, commercial detection has been excellent but I do have to
>> add the occasional cut.
>> Most of my own edits work fine, but some do have brief 1-second
>> flashes of commercial. I've just been adding cuts at the black frames,
>> but what should I be doing to finesse my cuts?
> My understanding is, that you can only cut at keyframes and that's what
> I do. So instead of moving frame by frame you should move keyframe by
> keyframe and set the beginning of the cut at the last keyframe before
> the commercial and the end of the cut at the first keyframe after the
> commercial.
> Thomas

I suspect that the answer to this question will depend on where you are 
and what hardware you use.  ISTR that mythtranscode --mpeg2 lossless 
editing used to decode and recode around cutpoints to give 
frame-accurate editing, but in my experience, now some years distant, it 
used to fail often with broadcast material.  For some time I 
preprocessed recordings with mencoder and then edited, but that still 
gave occasional failures - eg loss of sound midway through a MythArchive 
dvd - that weren't apparent until later.  Now, as I keep saying, I use 
Project-X to do all this.  It doesn't give frame-accurate cutting - the 
logs say 'dropping useless B-frames' at most cutpoints - but it 
certainly seems less coarse-grained than editing only at keyframes, and 
failures of any kind are almost unknown.  YMMV.  I haven't cared enough 
about this recently to try lossless mythtranscode after Project-X;  it 
might work for direct viewing but I suspect that further processing 
might still run into difficulties.

If your main aim is to reduce filesize without transcoding with a 
different codec you may find several streams that you don't really need. 
  Removing these from eg a BBC SD recording often shrinks it quite a lot.

Or, back to your original question, you could look at Robert McNamara's 
page here, which I suppose is still relevant.



John P

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