[Libav-user] JPEG decoder

cyril apan cyrilapan at yahoo.fr
Thu Jun 13 11:07:04 CEST 2013

>Hi All

>When using the JPEG decoder (CODEC_ID_MJPEG) sometimes I find that decoded frames are inverted/upside down/back to front. Having read into the problem I believe the issue is to do with the fact that bitmap is sometimes stored bottom-up in JPEG files.

>Does the decoder not realign the frame correctly or is this something that I would have to take care of after the decoding? If anyone can suggest the best way to deal with this I would appreciate it.

You'll have to read metadata (Exif most of the time) to know what is the orientation of the stored bitmap and then process it to get the right rendering.
I don't think ffmpeg has any facility to read Exif metadata but you can use filters to do the rotation/flipping job.


Cyril APAN.
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