[mythtv] DVB, HD-2000, and CRCs

[Taylor Jacob]

Quoting Daniel Thor Kristjansson <danielk at mrl.nyu.edu>:

> CRC-32 is robust against 1 bit errors, and should be robust against
> multiple bit errors caused by random error sources. I'm actually
> surprised that the driver is doing CRC checks, since you have to
> assemble an entire PES Packet to check the CRC (i.e. you need about
> 2.5 MB of buffers for 20 streams). With the pcHDTV drivers I only
> bothered to do this for PSIP tables.

If you look at the dvb driver API and the code in question, you will see that
the demux driver does section reassembly in software and or hardware (depending
on if your transport ic can do it in hardware or not).  It is ONLY for section
data the dvb driver does CRC validation.. This is a reasonable thing so CRC
checking does not need to be implimented in every application.. Now validating
that the content of the tables is not a low level verification, which I have to
do if the table passes CRC32.. Since validating the structure of an ATSC table
goes beyond the scope of the driver set..

> BTW you can tell ffmpeg to check the PES Packet CRC's on playback, but
> we're not currently doing this.

Its not an ffmpeg issue either, since the EIT doesn't get written to any
recordings since its worthless information as far as recording a television
show is concerned..  All of this is handled in recorder and siparser on the
backend not the frontend..

Taylor