[FFmpeg-devel] [PATCHv2] add signature filter for MPEG7 video signature

Gerion Entrup gerion.entrup.ffdev at flump.de
Wed Mar 30 13:57:24 CEST 2016

Attached improved version of patch.

Differences to last time:
- reduce amount of errors in the signature (the last patch included some int
foo = a/b). This version replaces this with a rational.
- implement binary output.
- fixes in configure, some typos

I have found the conformance testfiles [1]. Both the binary and the xml output
passes the conformance test but are not bitexact. I wrote some python script
to prove this (see attachment). I don't see why this happens. If someone want
to help, the correspondent reference code is in the file
"ExtractionUtilities/VideoSignatureExtraction.cpp" beginning with line 1615,
that could be found here [2].

Then a few questions:
- The timebase of the testfiles is 90000. In the binary output unfortunately there
is only place for a 16 bit number, so this don't fit. Currently the code simply crop
remaining bits. Is there a better solution (devide with some number etc)?

- I try to use put_bits32 where it is possible, because I thought is is faster. Then
I saw it internally uses put_bits as well. Does it have a performance impact to
replace it with put_bits(..., 8, ...) (would simplify the code a lot)?


[1] http://standards.iso.org/ittf/PubliclyAvailableStandards/c057047_ISO_IEC_15938-7_2003_Amd_6_2011_Conformance_Testing.zip
[2] http://standards.iso.org/ittf/PubliclyAvailableStandards/c056735_ISO_IEC_15938-6_2003_Amd_4_2011_Electronic_inserts.zip
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