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

[Don Moir]

----- Original Message ----- 
  From: Alex Cohn 
  To: This list is about using libavcodec, libavformat,libavutil libavdevice and libavfilter. 
  Sent: Friday, July 26, 2013 3:01 PM
  Subject: Re: [Libav-user] Some input files decoded upside down.


  On Jul 26, 2013 9:53 PM, "Jason Cipriani" <jason.cipriani at gmail.com> wrote:
  >
  > 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

  The linesize [] parameter should contain a negative value indicating image is flipped
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