Contrary to what you claim below, this seems not to have worked:
You dropped frames which is typically no intended.
What is wrong with the file you have?
> video:4138930kB audio:289208kB subtitle:0kB other streams:0kB global
> headers:0kB muxing overhead: 0.068010%
> And that seems to work.
> My questions:
> Is there a way to de telecine without reencoding ?
When you stream-copy with FFmpeg, soft-telecine gets
lost because FFmpeg doesn't support it.
> If I have to reencode, does Stream #0:0 -> #0:0 (mpeg2video (native) ->
> mpeg2video (native)) actually reencode. Or does it just copy the frame
> content ?
It is definitely re-encoded and because of the nature of mpeg2video,
this cannot be lossless.