[mythtv-users] H264 conversion of interlaced MPEG2?

[Stephen Worthington]

On Tue,  5 May 2015 18:17:05 -0400 (EDT), you wrote:


>Questions for anyone:
>(a) Is there some way of forcing mythfrontend to assume something is
>    interlaced if it's not?  E.g., to apply deinterlacing?  This will
>    be useful to the OP and perhaps myself (once I'm using a current
>    mythfrontend).

Yes.  While playing (or paused), M (menu) > Video > Advanced > Video
Scan and then select from Detect, Progressive, Interlaced (Normal),
Interlaced (Reversed).  The "Detect" menu item shows a (P) after it
normally, which I presume indicates what mythfrontend detected as the
mode for the file.

Then, if playing back in an interlaced mode,  M (menu) > Video >
Advanced > Deinterlacer and choose your deinterlacer - it defaults to
None for me, which I consider to be a bug - it should automatically
choose the deinterlace mode I have specified in my setup.

This option is unfortunately only available after you start playing an
individual file and is not stored for the next time you start playing
it.

>(b) Is there some way of producing interlaced output with my current
>    hardware short of installing the latest myth on the machine (that
>    machine has no myth right now) and seeing what that does?  I'm
>    really trying to figure out if retranscoding what I've already
>    done---but this time in MBAFF---is going to have benefits down the
>    road, e.g., when I'm really using a modern mythfrontend to feed an
>    interlaced CRT display.

There is probably a way of creating interlaced output modes using
xorg.conf, but it is likely a pretty complicated process to produce
the correct modelines if they are not created automatically.  If it is
not happening automatically, it is likely that the EDID data from your
CRT (TV? monitor?) is not providing any interlaced modes, and that can
indicate that it is, in fact, not capable of interlaced modes.  But it
is more likely that the manufacturers simply did not bother to put in
the interlaced modes as "no-one ever needs interlaced when using a
screen as a computer monitor".

>(c) In my final configuration of latest released myth + some nvidia
>    card, can I in fact produce interlaced output?  If the card has
>    S-Video or some other (component? composite?) output, can I be
>    reasonably assured it can actually send interlaced video to it?
>    I can't test this yet.  (I'm assuming card VGA out->VGA scan
>    converter means it's progressive out the VGA & hence not what I
>    want.)  I recall something from years ago about nvidea cards'
>    firmware losing the ability to actually output interlaced, but
>    I don't know if that's right or is still true.

I do not know the answer to that question either.  I have not
seriously tried to ever output interlaced to my TV, as everything
seems to be set up on the assumption that interlacing should be
removed at the earliest opportunity.  In theory, doing a conversion to
progressive when re-encoding should be able to produce a better result
than anything done at playback time as it does not have to be done in
real time and hence can use as much processor as is needed to get the
best result.  It is really only with CRTs that there is any benefit
from leaving things interlaced, as the CRT itself will display them
interlaced and let the human eye do the merging of the interlaced
frames.  Once you get an LCD TV, the TV will have to do the
deinterlacing before displaying the picture, although some do have
very good real-time deinterlacing in their chipsets.  So my suggestion
would be that you should do the deinterlacing in the best way possible
as part of your transcoding process and just put up with the slowdown
it causes in the process, as that will give the best result.

As an aside, are all the recordings you are working on all using the
same interlacing (top field first or bottom field first).  If not,
then you will need to detect what is in the file and use the right tff
or bff settings.