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

Jason Cipriani jason.cipriani at gmail.com
Tue Jul 23 18:52:10 CEST 2013


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?

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