[Libav-user] Some input files decoded upside down.

[Jason Cipriani]

On Fri, Jul 26, 2013 at 2:40 PM, Alex Cohn <alexcohn at netvision.net.il>wrote:

> On Jul 23, 2013 7:52 PM, "Jason Cipriani" <jason.cipriani at gmail.com>
> wrote:
> >
> > Hello,
> >
> > I'm learning how to use libav. I'm following the tutorial at
> http://dranger.com/ffmpeg/tutorial01.html and have been able to read
> files, decode them, and save each frame to an image just fine. However,
> certain input files lead to the frames being decoded upside down (the input
> files play correctly in, say, mplayer).
> >
> > I have one input file that uses a rawvideo codec. This is decoded upside
> down. I have another input file that uses h264, this is decoded in the
> correct orientation.
> >
> > My question is, is there a flag in some *Context somewhere that
> indicates that the video frames are bottom-up, so that I can flip
> vertically if necessary when processing the frames after decoding?
> >
> > Also, then, it's easy enough for me to process an image upside down if
> necessary, but can sws_scale (or something similar) flip an image
> vertically so I can do the flip and RGB conversion all in one step?
> >
> > Thanks!
> > Jason
>
> Yes, you can perform flip and color conversion in one step with sws_scale.
> You can find the answer in this thread:
> http://ffmpeg-users.933282.n4.nabble.com/Flip-in-sws-scale-td939665.html
>
> BR,
> Alex
>
>

Thanks! That answers my sws_scale question.

My remaining problem is: How can I tell if the video needs to be flipped
vertically or not? Is there a flag in one of the context structures
somewhere? I have some input files that end up vertically flipped, and some
that do not, but I'm sure the information exists somewhere because when I
play those files in media players, the players are able to play them all in
the correct orientation.

Thanks again for your time,
Jason
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