Stripping first 32 bytes isn't gonna work reliably with different files. you are assuming that first flv packet is 'AVC sequence header' and it's of same length for different files which isn't true. a better way to join those files is explained below:
1. create a new folder (BeatConvert) and copy
BeatConvert.php,
FlvFixer.php,
FFMpeg.exe to this folder.
2. now create a new bat file (BeatConvert.bat) with following content:
Code:
if exist "List.txt" del "List.txt"
for %%a in (*.beat) do php BeatConvert.php %%a && echo file '%%~na.flv' >> List.txt
FFMpeg.exe -y -f concat -i List.txt -c copy Final.flv
php FlvFixer.php --in Final.flv --out Final_fixed.flv --nometa
FFMpeg.exe -y -i Final_fixed.flv -c copy Final.mkv
3. now copy your beat files (0000.beat....nnnn.beat) to the same folder and run the bat file.
if everything goes as expected a new file (Final.mkv) will be created which should be in sync.