Add a post-process-file hook to ffmpeg_converter_convert_filefield().

Add a post-process-file hook to ffmpeg_converter_convert_filefield(), right after the execution of the ffmpeg_converter_convert() call.

I need to process the flv-file with flvtools. I didn't thought about chaining the flvtool2 command to the ffmpeg command as in #631012: Conversion fails with chained custom commands. Anyway, it seems to be a hack, because ffmpeg_converter don't know how the ffmpeg command will be executed in future. What I want is to post process the file by another module after the conversion. Therefore I would like to see a post process hook. Okay, there is a hook_ffmpeg_converter_success(), but I don't like to use it because it is executed after field_file_save_file().

What do you think about invoking this hook?