[Libav-user] Help with unpacking PIX_FMT_YUV4* data types

Ricky Huang rhuang.work at gmail.com
Tue Mar 11 00:18:27 CET 2014

Hello all,

I am writing code that extracts the luminance component of an input video using my own custom filter in libavfilter - specifically I am extracting it from "PIX_FMT_YUV420P" a video and I am wondering how to go about doing so.  According to the pixfmt.h header: 
> PIX_FMT_YUV420P,   ///< planar YUV 4:2:0, 12bpp, (1 Cr & Cb sample per 2x2 Y samples)

I am not sure how to interpret that.  Assuming I am doing this in my draw_slice() function. It has the definition of:
> static void draw_slice(AVFilterLink *inlink, int y0, int h, int slice_dir)

I know I can get to the input data plane by:
> AVFilterBufferRef *cur_pic = link->cur_buf;
> uint8_t *data = cur_pic->data[0];

But there are multiple "planes" in the data.  Does data[0], data[1], data[2] correspond to each of the Y, U, V channels?

Also, once I am able to point my pointer at the correct coordinate, how should I interpret the extracted result (float, int, etc)?

Thank you in advance.
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