Auravision

• FourCCs: AURA, AUR2
• Company: Auravision
• Samples:
  • AURA: http://samples.mplayerhq.hu/V-codecs/AURA/
  • AUR2: http://samples.mplayerhq.hu/V-codecs/AUR2/

According to various codec lists, AURA is a YUV 4:1:1 codec while AUR2 is YUV 4:2:2. The payload of an AURA frame begins with the 6 ASCII bytes 'YUV411'.

Note from former Auravision Employee (but not aura/aur2 codec developer): Aura codec is not compression one (i.e. mpeg), but rather color space conversion.

Hypothesis

--Multimedia Mike 02:42, 10 December 2008 (EST)

Any given AURA sample contains frames of a constant size. For 160x120 files, the frames are each 14448 bytes. For 240x180 files, the frames are each 32448 bytes. In YUV 4:1:1 data, a 4x4 block consisting of 16 pixels assigns a Y sample to each pixel while all 16 pixels share a U and a V sample. If each sample is 1 byte, the size of a raw YUV 4:1:1 frame is (width * height * 18) / 16. This formula does not reconcile with AURA frames.

However, if each of the Y samples is only coded with 5 bits, the observed frame sizes come close, with 48 extra bytes. Indeed, the frames do appear to begin with a 48-byte header. So the size of the frame is calculated as

 p = width * height
 48 + (p * 5/8) + (p/16) * 2

Testing this hypothesis might require trying several different bit reading methods.

Hypothesis 2

--Kostya 06:07, 10 December 2008 (EST)

first 16 bytes - some rubbish
next 16 bytes - quantization table for luma
next 16 bytes - quantization table for chroma

the rest is packed into nibbles somehow with actual value obtained via table

Hypothesis 3

--Multimedia Mike 14:17, 10 December 2008 (EST)

I move to strike my earlier hypothesis (though I'm amazed that the numbers worked out). I was confusing YUV 4:1:1 with YUV 4:1:0. YUV 4:1:1 carries as much chroma information as YUV 4:2:2, just in a different orientation. Thus, there are 1/4 as many chroma samples as luma samples, rather than 1/16.

I support Kostya's hypothesis. The revised size calculation would be:

p = width * height
48 (bytes) + 
( p (luma samples) * 4 (bits/luma sample) / 8 (bits/byte) ) +
( p/4 (chroma samples/chroma plane) * 4 (bits/chroma sample) / 8 (bits/byte) ) * 2 (chroma planes)

Which reduces to:

total bytes/frame = 48 + (3 * p / 4)