[mythtv-users] HD PVR 2 and mythtv

Devin Heitmueller dheitmueller at kernellabs.com
Thu Mar 31 17:20:01 UTC 2016


> You are probably right in that it will just encode the incoming frames with
> some fixed set of parameters but it is possible to re-compress video streams
> that originate from MPEG or H.264 without losing any information. The only
> lossy step in encoding is the quantization conversion and if you know the
> coefficients used in the original compression you can reuse them and you
> don't get generational loss. You have to do that per macroblock and know
> where the i-frames are located.

Yes, in the transcode use case where you have access to the state
machine for the decoder there are indeed some games you can play to
reuse the quantization coefficients.  That said, in the case of the
encoder products discussed in this thread, the device is receiving
uncompressed video (i.e. over the HDMI link), there is no access to
any such decoder state information from the original stream.

> I worked on an ASIC for a nameless Japanese electronics mega-corporation
> that was to be used in a video mixing desk. Some of the inputs would be from
> MPEG and H.264 streams and the aim was to re-encode without loss. Don't know
> if you can buy it but it was a whopper of a chip and meant for broadcasters.

Most of the major silicon vendors for broadcast transcode have this
functionality (i.e. Vixs, Zenverge, Fujitsu, to name a few).

Devin

-- 
Devin J. Heitmueller - Kernel Labs
http://www.kernellabs.com


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