[Spice-devel] [PATCH spice-server 00/28] adaptive video streaming

[Hans de Goede]

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