[mythtv] mythtv commit: r8651 by danielk (Auto Aspect Ratio transcode)
jonese at zener.com
Thu Jan 19 23:53:13 UTC 2006
> On 19 Jan 2006, at 22:42, Endaf Jones wrote:
> >> Modified:
> >> trunk/mythtv/libs/libmythtv/videobuffers.cpp
> >> Log:
> >> Fixes #1053.
> >> In this case an MPEG-4 recording is using a frame height which is not
> >> a multiple of 16. ffmpeg isn't doing any validation on the dimensions
> >> so it ends up writing outside the buffer. This just pads allocated
> >> buffers up to multiples of 16, so that this type of error doesn't
> >> cause
> >> a segfault with any of the codecs we support. MythTV does prevent you
> >> from setting an invalid dimension when you record to a MPEG-4 NUV, so
> >> AFAIK this is more of a legacy issue.
> > Question..
> > What about transcoding MPEG2 into MPEG4 after a recording and you have
> > "Resize Video while transcoding" AND the newly developed "Preserve
> > Aspect Ratio of Video when resizing" option? The height is auto
> > calculated in that case.
> > Is this situation the same as the above commit?
> > I say this because I have a PBS HDTV program 1920x1080i that I
> > transcode into a 544 wide MPEG4 so I can view it on my SDTV. The
> > height works out to be 302 or so pixels (to keep the aspect correct).
> > When I play that newly encoded file, I have a strange color cast on
> > the top 1/6th of the picture.
> > Same problem or different?
> > --
> > # Endaf
On 1/19/06, Dave Just <justifiably at cwazy.co.uk> wrote:
> Yes! This is just the situation I had. I have my low quality
> transcode settings to rescale from usual capture resolution of
> 720x576 down to 480x384. Both multiples of 16. But then I also
> added the "Preserve aspect option" when it appeared. The result was
> that some of my captures which are at 4:3 instead of 16:9 got scaled
> to a larger height, 392, not divisible by 16... and yes, the
> transcoded files have fuzzy green borders in the top 1/6th or so.
> I'm disabling the "preserve aspect ratio" for now again. Maybe that
> option needs tuning to enforce the standards. (BTW, wouldn't it be
> better to scale the width according to the desired height anyway? I
> think it's more useful to specify vertical resolution to match output
Glad to see I wasn't the only one with a strange color overlay at the top.
I also wondered if there is value in fixing the aspect ratio to the
height instead of the width (or have the option between the two).
More information about the mythtv-dev