Hi Alex,
I do a lot of work creating filters for ffmpeg and other YUV based
video libraries.
When doing a rotate, there are 2 gotchas you have to be aware of.
1) Chroma subsampling. Anything that has a different vertical
sampling to horizontal will cause problems for rotation. EG chroma
subsampling such as 422, 411 and 410 will cause problems. (444 and 420
should be ok)
2) interlaced video. If your video is from an interlaced source you
will have a great deal of headaches.
The video data is pretty simply stored.
It's 3 planes of data, one for Y one for U and one for V.
Which are referenced in the AVFrame struct as data[0], data[1] and
data[2]
To determine your X and Y location in the data you multiply the Y by
the linesize
eg
pixel = *((AVFrame->data[0])+y*AVFrame->linesize[0]+x);
Due to chroma subsampling the size of the U and V planes will be
smaller than the Y. 444 video has no chroma subsampling.
Here's a quick table to illustrate how the subsampling affects the
chroma plane size, using a video size of 720x576.
444 720x480
422 360x480
411 180x480
420 360x288
410 180x288
The chroma pixel (UV) refers to a number of luma pixels (Y)
It'd be a good idea learning how these pixels are arranged.
Any questions, feel free to ask.
I hope this helps.
Mark
On 02/11/2010, at 8:30 AM, [email protected] wrote:
sorry for the newbie questions....
I need to perform 90 degree rotation of each AVFrame. I need to do
it programmatically rather then using filters on ffmpeg command
line. I was trying to understand how to do it, but unfortunately
there is not much details on AVFrame.data and linesize elements. I
am using YUV_420 format and I understand there will be only 3
references in data and linesize. That is as far as I got. Any
information would be greatly appreciated.
Alex_______________________________________________
libav-user mailing list
[email protected]
https://lists.mplayerhq.hu/mailman/listinfo/libav-user
_______________________________________________
libav-user mailing list
[email protected]
https://lists.mplayerhq.hu/mailman/listinfo/libav-user
