Hi,
On 02/27/2013 03:01 PM, Yonit Halperin wrote:
On 02/26/2013 02:49 PM, Marc-André Lureau wrote:
----- Mensaje original -----
Hi,
On 02/26/2013 01:40 PM, Marc-André Lureau wrote:
Hi
----- Mensaje original -----
The adaptive video streaming is implemented by the following
heuristic:
Given a bit rate, we calculate the best combination of mjpeg
quality
and frame rate (henceforth, the stream parameters) for this
bit rate. In order to decide this combination, we evaluate the
encoding size for different jpeg
qualities by applying them on successive frames.
But no downscaling?
Good point. However, the default libjpeg sampling factors values are
already 2 for luminance components and 1 for chrominance components
(both horizontal and vertical), while 4 is the highest value, and
larger
factor means higher resolution. It is worth trying decreasing the
luminance to 1.
According to wikipedia, the jpeg YUV downscaling is:
"The ratios at which the downsampling is ordinarily done for JPEG images are 4:4:4 (no downsampling), 4:2:2 (reduction by a factor of 2 in the horizontal direction), or (most commonly) 4:2:0"
So luminance is not downsampled. Is that what you said? According to my experience with video codecs (not so much with jpeg itself), downsampling really makes a difference to most codecs, both in term of overally quality and cpu usage.
I understand from libjpeg documentation that by default the luminance is downsampled by a factor of 2, and the chrominance by a factor of 4. So we can try downsampling the luminance by a factor of 4.
I think you're misreading the docs then. Standard jpeg's have there luminance
data not downsampled *at all*, so the y channel is at full res of the original
picture.
Regards,
Hans
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