CVE-2025-59729 Heap-buffer-overflow read in FFmpeg DHAV get_duration

When parsing the header for a DHAV file, there's an integer underflow in offset calculation that leads to reading the duration from before the start of the allocated buffer. If we load a DHAV file that is larger than MAXDURATIONBUFFERSIZE bytes 0x100000 for example 0x101000 bytes, then at 0 we ha...