Root Cause Analysis: Looking at the given vulnerable code line and its context, the CWE-787 (out-of-bounds write) vulnerability exists in the code because the `init_get_bits` function is called with `ptr_len * 8` as the bit length parameter. However, `ptr_len` is calculated as `src_len - 1 - byte * 2`, which can potentially be negative if `byte * 2` is greater than `src_len - 1`. In this case, `ptr_len * 8` will result in a negative value, which can lead to an out-of-bounds write when `init_get_bits` initializes the `GetBitContext` structure with an invalid bit length. This can cause memory corruption and other undefined behavior, which is a CWE-787 vulnerability.