This is flvlib (with some very minor modifications) ported to Python3.
flvlib is a library for manipulating, parsing and verifying FLV
files.  It also includes two example scripts, debug-flv and index-flv,
which demonstrate the possible applications of the library.

If you got the source tarball, you can run the automated test suite
and install the library with:
$ tar xjf flvlib-x.x.x.tar.bz2
$ cd flvlib-x.x.x
$ python setup.py test
$ sudo python setup.py install

After that you can debug FLV files with:
$ debug-flv file.flv

and index them with:
$ index-flv -U file.flv

Try:
$ debug-flv --help
$ index-flv --help
for more available parameters.

The library and the scripts are distributed under the MIT License.
The original author is  Jan Urbanski, at wulczer@wulczer.org.
The Python3 port was done by Tivadar Szemethy, 
tivadar dot szemethy at gmail.com