int ff_combine_frame(ParseContext *pc, int next, const uint8_t **buf, int *buf_size)
{
    if(pc->overread){
        av_dlog(NULL, "overread %d, state:%X next:%d index:%d o_index:%d\n",
                pc->overread, pc->state, next, pc->index, pc->overread_index);
        av_dlog(NULL, "%X %X %X %X\n", (*buf)[0], (*buf)[1], (*buf)[2], (*buf)[3]);
    }

    /* Copy overread bytes from last frame into buffer. */
    for(; pc->overread>0; pc->overread--){
        pc->buffer[pc->index++]= pc->buffer[pc->overread_index++];
    }

    /* flush remaining if EOF */
    if(!*buf_size && next == END_NOT_FOUND){
        next= 0;
    }

    pc->last_index= pc->index;

    /* copy into buffer end return */
     if(next == END_NOT_FOUND){
         void* new_buffer = av_fast_realloc(pc->buffer, &pc->buffer_size, (*buf_size) + pc->index + FF_INPUT_BUFFER_PADDING_SIZE);
 
        if(!new_buffer) {
            pc->index = 0;
             return AVERROR(ENOMEM);
        }
         pc->buffer = new_buffer;
         memcpy(&pc->buffer[pc->index], *buf, *buf_size);
         pc->index += *buf_size;
        return -1;
    }

    *buf_size=
    pc->overread_index= pc->index + next;

     /* append to buffer */
     if(pc->index){
         void* new_buffer = av_fast_realloc(pc->buffer, &pc->buffer_size, next + pc->index + FF_INPUT_BUFFER_PADDING_SIZE);
        if(!new_buffer) {
            pc->overread_index =
            pc->index = 0;
             return AVERROR(ENOMEM);
        }
         pc->buffer = new_buffer;
         if (next > -FF_INPUT_BUFFER_PADDING_SIZE)
             memcpy(&pc->buffer[pc->index], *buf,
                   next + FF_INPUT_BUFFER_PADDING_SIZE);
        pc->index = 0;
        *buf= pc->buffer;
    }

    /* store overread bytes */
    for(;next < 0; next++){
        pc->state = (pc->state<<8) | pc->buffer[pc->last_index + next];
        pc->state64 = (pc->state64<<8) | pc->buffer[pc->last_index + next];
        pc->overread++;
    }

    if(pc->overread){
        av_dlog(NULL, "overread %d, state:%X next:%d index:%d o_index:%d\n",
                pc->overread, pc->state, next, pc->index, pc->overread_index);
        av_dlog(NULL, "%X %X %X %X\n", (*buf)[0], (*buf)[1],(*buf)[2],(*buf)[3]);
    }

    return 0;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.