Re: [Fame-devel] YUV MPEG encapsulation

[Vivien C. <vi...@ne...>]

Hi,

> Many people re-encode non MPEG 1/2 data to MPEG-1/2 when using mplayer
> with their dxr3 (http://dxr3.sourceforge.net) video card.
> 
> This has two major drawbacks:
> 1. Quality loss because of the re-compression
> 2. CPU time lost for the re-compression

indeed.

> I'm currently (re-)writing a patch for SDL (http://www.libsdl.org)
> to add dxr3 support by generating MPEG frames.
> 
> While coding I had the following idea:
> Would it be possible (and fast?) to just encapsulate the YUV (even RGB?)
> data as MPEG frames with nearly no compression applied?

It is possible not to lose quality (lossless compression) by chosing a
high quality value (90-100%), but it still requires a bit of
computation. In order to produce a valid MPEG stream you still have to do
the most time consuming part of the compression algorithm which is the DCT
and bitstream writing. The DCT and quantization steps do not scale
depending on quality (always the same time to perform), whereas the
bitstream writing step would be even slower (because at high quality there
are more bits to write). So, the fastest you can do is code at very low
quality, the best you can do is code a very high quality at the cost of
CPU time.
MPEG has no support for uncompressed (either RGB or YUV) streams.

regards,
Vivien.