[FFmpeg-user] compressed data with sdti

[Dave Rice]

On Oct 3, 2012, at 6:51 PM, Carl Eugen Hoyos wrote:

> Dave Rice <daverice <at> mac.com> writes:
> 
>> I tried capturing an SDTI output of a video deck to 
>> an SDI capture card to an uncompressed file. I see 
>> that the encoded data is stored in a single field of 
>> this resulting v210 codec so I hoped to take only 
>> that single field and parse out the compressed data 
>> (mpeg2 from the tape); however in the resulting data 
>> I see none of the usual identities of mpeg2 (gop 
>> headers, 0x0001b5, etc).
> 
> Is there a tool that allows to extract the MPEG2 data?

The only tools I know of that do this are digital videotape recorders that would have an SDTI input.

> Because if yes, it should be possible to find out how 
> it is done.

I suspect that SDTI is not anticipated to capture as SDI as I've done. SDI using a linear feedback shift register to scramble then unscramble the data during transmission. It seems that a receiver of an SDI stream needs to process the data through two linear feedback shift registers (see page 60 here http://china.xilinx.com/support/documentation/application_notes/xapp514.pdf) in order to decode the SDI data. One guess I have is that the SDTI data is never scrambled in the first place thus the SDI capture card I have is trying to unscramble data that may not need it. This is a theory but I suspect that if SDTI is ingest via SDI at 10 bit uncompressed than it could be unscrambled via the lfsrs to obtain the compressed data payload of the SDTI. This would then be either mpeg2 or dv within packets plus some parity data.

> If not: Are you sure it is possible at all?

:) I suspect it is possible but not necessarily easy. This certainly makes me appreciate the more accessible digital video tapes like DV.
Dave